NES BASIC Programming Guide

1. Welcome to NES BASIC

A small computer can be a good place to learn programming. You type a line, run it, and see exactly what changes. NES BASIC turns an NES cartridge into that kind of computer: a language, a text editor, a graphics canvas, hardware sprites, sound and a small project library, all running on the emulated NES processor.

8-Bit Impostor provides the host screen, touch controls, controller connections, optional external-keyboard transport and persistent battery files. It does not evaluate BASIC for the cartridge. The same standalone ROM has its own controller keyboard and interpreter. The PDF you are reading is a host document, not an NES program; a physical NES does not display this book.

This is a deliberately small integer BASIC. There are single-letter numeric variables and independent single-letter string variables. Numeric arrays add one- and two-dimensional tables. There are no floating-point numbers, string arrays, ELSE, DATA/READ or ON GOTO. Its limitations are useful to know early: they make your programs easier to plan and your errors easier to fix. The feature matrix in the appendices describes this edition rather than another BASIC dialect.

BASIC, NES PAINT, EDITOR, CALCULATOR, NES SHEETS, BLOCKDROP and ASTRO BLASTER are separate cartridges in NDB SOFTWARE. Opening BASIC does not depend on opening Paint, and their saved projects are not shared. This guide concentrates on BASIC.

You can keep a finished image or sprite visible when a program ends. You can also interrupt a loop, return to editing and run it again. Use explicit SAVE to keep source and artwork before resetting or leaving. Saving a program is different from saving an emulator snapshot; Chapter 12 explains both.

2. Quick start: type, run, keep

In the browser, open the playground. The actual cartridge boots and prints its welcome and READY. In the iOS app, open NDB SOFTWARE, choose NES BASIC, then PLAY / RESUME. Press Select to open the on-screen keyboard. Move with the D-pad, insert with A, backspace with B and submit with Start. On an external keyboard, type normally and use Enter. Submit each numbered line separately.

10 PRINT "HELLO FROM NES BASIC"
20 END

Now submit RUN. The output is HELLO FROM NES BASIC. Submit LIST to see the two stored lines. A number at the start stores a line; an unnumbered submission is a direct command. The number is an address in your program, not part of the printed message. Leaving gaps of ten makes it easy to insert lines later.

To change the message, resubmit line 10 with a different quoted string. To delete line 20, submit 20 by itself. The editor is a line editor, not a full-screen source editor: LIST displays stored code, and you replace a stored line by typing its number and new contents. Source is kept sorted by line number.

Submit SAVE "HELLO" and wait for SAVED "HELLO". After a cold start, use LOAD "HELLO", then RUN. RUN "HELLO" loads and runs the named file in one step. If a confirmation appears, A/Y/Enter accepts; B/N/Select/Escape cancels. A saved file includes your program and all kept BASIC artwork.

READY is printed at startup. Successful ordinary commands return quietly to the editing cursor; the lack of another READY message is normal. Errors show a message and return to editing. For a runtime error, IN 100 identifies the source line where execution failed. Correct that line and try RUN again.

3. The editor and its keyboards

The native keyboard has letter and symbol pages. SHFT changes pages; SPCE inserts a space. Select opens or closes it without submitting the current line. With the keyboard open, the D-pad chooses keys. With it closed, Left/Right moves the caret through the current line. Reopen it to insert at that position. B removes the character before the caret. Insertion moves the rest of the line to the right.

The input line accepts at most 95 characters and wraps on the 28-column editing area. That physical input limit is separate from the tokenized program capacity. A stored line also needs its line number and record metadata. A string variable has a smaller, separate limit of 63 bytes; do not confuse these limits.

External keyboard input follows the same ROM editor. Enter submits, Backspace deletes, Escape closes the controller keyboard, Left/Right moves the caret, and Cmd+Left/Right goes to the start/end. Ctrl+C interrupts a running program. Source entry normalizes lowercase letters to uppercase, including characters entered inside string literals. There is no Unicode source editor. The browser playground adds Load .bas and numbered-listing paste support; imports are validated by the actual ROM before replacing your working program. The iOS guide describes entering listings as separate submissions.

The optional external-keyboard bridge uses virtual controller port two. After its handshake, JOY(2) returns zero until reset. It is not the original Family BASIC keyboard protocol. You can always use the on-screen keyboard with ordinary NES controller input, including in another compatible emulator.

NEW clears working source and variables after confirming a nonempty dirty program. It keeps your kept artwork. CLEAR resets values and control state while keeping source and artwork. RUN starts from the beginning and resets variables. Use LIST to review a program before replacing it. Long LIST/output pauses after 18 rows: Start continues and Select cancels with BREAK.

4. Language fundamentals

Numbers are checked signed 16-bit integers: -32768 through 32767. A division truncates toward zero, so -7/3 is -2. Overflow raises OVERFLOW rather than silently wrapping. Dividing by zero raises DIVISION BY ZERO. Integer INT is an identity operation; the language has no decimal fraction type to round.

There are 26 numeric variables, A through Z. Assignment can be written A=42 or LET A=42. A variable defaults to zero. Multi-letter names such as TOTAL and names with digits such as X1 are unsupported. Choose a letter and use REM to say what it means. String A$ and array A(...) are separate from numeric scalar A.

Expressions support unary +/-, multiplication/division, addition/subtraction, parentheses and comparisons. Precedence is unary, then multiply/divide, then add/subtract or string concatenation, then comparisons. For example, 2+3*4 is 14; (2+3)*4 is 20. Comparisons = <> < > <= >= produce numeric 1 for true and 0 for false. There are no AND/OR/NOT or bitwise operators in this edition.

A colon separates statements on the same source line. REM ignores the remainder of its line, including colons and words that would otherwise be keywords. Use comments for intent and units. Keywords inside a quoted string are text. Unclosed double quotes raise SYNTAX ERROR. Extra punctuation is not ignored.

Line numbers range from 1 to 65535, independently of the signed numeric value range. A program holds at most 128 lines and 3072 tokenized source bytes. Keywords are compact tokens, so typed character count is not the same as stored byte count. The expression parser has a guarded nesting limit, and FOR/GOSUB share an eight-frame control stack. Keep expressions and nesting modest.

Numeric arrays: a board of values

DIM allocates an array before you use it. Each name is one letter, A through Z. Indexes start at zero and upper bounds are inclusive: DIM B(9,19) creates 10 columns by 20 rows, or 200 signed 16-bit cells. DIM A(4) creates five cells, A(0) through A(4). Every new cell starts at zero. There are no string arrays.

Assign with B(4,19)=7, then read with PRINT B(4,19). Indexes may be numeric expressions or other array reads. LET B(X+1,Y)=B(X,Y)+1 is valid when the computed indexes are within both bounds. Two-dimensional storage is row-major: the second index varies fastest. A scalar B, string B$, and array B(...) are independent. FOR/NEXT counters remain scalar letters; INPUT can target a cell.

10 DIM B(9,19)
20 FOR X=0 TO 9
30 FOR Y=0 TO 19
40 B(X,Y)=X*20+Y
50 NEXT Y
60 NEXT X
70 PRINT B(0,0);" ";B(9,19)
80 END

The output is 0 199. This initializes all 200 cells through ordinary nested loops. Change line 70 to 70 PRINT B(4,19) to see 99.

All arrays share 1,216 cells (2,432 bytes). The board above uses 200 cells, leaving 1,016. Descriptor space for all 26 names is separate. A DIM statement allocates one array; use a colon or another line for another DIM. Use MEM to see remaining code bytes, lines, array cells and string-pool bytes. Use FILES for the six save slots; save space is separate from those working counters.

Bounds must be nonnegative integers. Negative bounds raise BAD ARRAY DIMENSION. Too many cells raise ARRAY SPACE FULL; fractional-looking syntax is rejected. Repeated DIM raises ARRAY ALREADY DIMENSIONED. Use CLEAR to release all arrays, then declare them again. There is no per-array resize or erase operation.

RUN, CLEAR, NEW, successful LOAD/LOADDEMO and reset release arrays along with ordinary variables. Put DIM in your numbered source so each RUN starts cleanly. END, STOP and a runtime error leave allocated cells available for inspection. SAVE and FILES preserve live arrays. Ordinary SAVE stores source and artwork, including DIM declarations; it does not save runtime array contents. Loading and running reconstructs the arrays from the saved program.

An undeclared array raises ARRAY NOT DIMENSIONED. Negative/out-of-range indexes, or the wrong number of indexes, raise SUBSCRIPT OUT OF RANGE. In a running program, the message includes the source line. Invalid DIM and failed stores preserve existing cells, artwork and committed saves. For interactive entry, try DIM A(0), then INPUT "CELL";A(0) and PRINT A(0).

Inspecting capacity

MEM prints the V1.1 version and free code bytes, line records, numeric array cells, and shared string bytes. Array counts are elements; multiply by two for payload bytes. String temporaries remain a separate 128-byte arena. FILES reports directory usage and the six source/art save slots. The source limit is still 3,072 tokenized bytes and 128 lines. An 8–12 KiB program target is future work requiring a reviewed memory/save design, not a current capability.

5. Strings and text values

A$ through Z$ are 26 string variables, independent of A through Z. They default to empty strings. String assignment, copying, concatenation and comparison are real typed operations. A$="HELLO", B$=A$ and C$=A$+"!" are valid direct fragments. The + operator concatenates strings only when both operands are strings.

Numeric and string values do not convert silently. A$=42, A=A$ or A$+1 raises TYPE MISMATCH. Use STR$ to make decimal text from an integer, or VAL to parse a whole decimal string. This makes a program's intended conversion visible.

An empty literal is "". To include a quotation mark, double it inside a literal: A$="SAY ""HI""" stores SAY "HI". String INPUT treats typed spaces and quotation marks as data rather than source syntax. Empty string input is valid.

All six comparison operators work between strings. Comparison is lexicographic on unsigned byte codes: an equal prefix sorts before a longer string. Thus "A" sorts before "AA". Comparison gives numeric 1/0. A string cannot be compared to a number without an explicit conversion. The uppercase-oriented font is not a Unicode collation system.

A stored or concatenated string can contain at most 63 bytes. All 26 variables share a compacted 256-byte pool. Empty strings use no pool bytes. Expressions also use a bounded 128-byte temporary arena. STRING TOO LONG means a result exceeds the length limit; STRING SPACE FULL means shared/temporary capacity is exhausted. The old destination survives a failed assignment. Shorten or clear values, or use CLEAR when it is safe to reset all values.

10 INPUT "YOUR NAME";N$
20 A$="HELLO, "+N$
30 PRINT A$
40 IF N$="" THEN PRINT "EMPTY NAME"
50 END

RUN, enter NES USER and submit. The result is HELLO, NES USER. RUN again and submit an empty answer: the program prints HELLO, followed by EMPTY NAME. The empty test compares N$ to an empty string, not to numeric zero. This listing is also the first complete project in Chapter 13.

6. Input and output

PRINT accepts numeric/string expressions and literal text. A semicolon places the next value immediately after the previous one. A comma advances to the next four-column tab stop. With no trailing separator, PRINT ends its output line. A trailing separator leaves the output position for the next PRINT. Comma is a formatting separator here; do not assume another BASIC dialect's larger zones.

PRINT "VALUE=";A prints the label and the number together. PRINT A;" ";A$ prints the independent numeric and string values with a space. These are direct fragments rather than complete stored programs. PRINT output has a bounded buffer; OUTPUT TOO LONG is recoverable.

INPUT accepts a numeric variable or a string variable, with an optional prompt expression and semicolon: INPUT "AGE";A or INPUT "NAME";N$. The cartridge adds its question marker. Numeric input must be a valid signed integer; an empty or invalid answer raises BAD INPUT and retries. String input preserves spaces and accepts empty input; overlong or pool-full entries retry without changing the old destination. B/Backspace edits the answer. Ctrl+C or the emergency pad gesture cancels and recovers.

LOCATE column,row positions text output at column 0–27, row 0–21. CLS clears the active text terminal or graphics canvas. PRINT, INPUT and LOCATE restore text when used from graphics, so they can remove a graphics image. Keep a program's graphics section and text reporting section distinct when that matters.

INKEY$ reads one newly queued input event without waiting; INPUT collects an edited whole answer and can wait. They serve different jobs. A loop using INKEY$ must test for an empty result before calling ASC. The input-code project in Chapter 11 shows the pattern.

7. Decisions, loops and subroutines

IF evaluates a numeric condition. A nonzero value is true. THEN can name a literal line target or start an inline statement. In a running program, IF A=1 THEN 100 jumps to line 100. IF A=1 THEN PRINT "YES" executes the inline PRINT. There is no ELSE. A false IF skips the entire remainder of its line, including colon-separated statements; put work that must always run on a different source line.

GOTO jumps to a literal line number. The target must exist. GOSUB jumps and saves a return location; RETURN resumes after that call, including a colon continuation. A missing target reports UNDEFINED LINE. RETURN without a matching call, or natural end of source while a GOSUB is still pending, reports INVALID RETURN. END/STOP intentionally terminate the program and discard pending control frames.

10 GOSUB 100
20 PRINT "BACK"
30 END
100 PRINT "IN SUBROUTINE"
110 RETURN

This prints IN SUBROUTINE, then BACK. The END prevents normal execution from falling into the subroutine. A subroutine is a convention using line numbers, not a separately declared function with arguments or local variables.

FOR/NEXT repeats using a numeric variable, inclusive limit and optional nonzero STEP. Positive and negative steps work. A loop whose initial value is already past its limit performs zero trips. NEXT names the same loop variable. Do not reuse an active loop variable for another FOR. A missing or mismatched NEXT reports UNMATCHED LOOP. FOR/GOSUB nesting together can use eight frames.

10 A=0
20 FOR I=1 TO 5
30 A=A+I
40 NEXT I
50 PRINT "TOTAL=";A
60 END

This prints TOTAL=15. After the loop, I is 6. Changing the step changes which values are added. Arithmetic that overflows while advancing a loop still raises OVERFLOW. To stop a runaway program, hold Start+Select for 60 emulated frames (about a second at normal NTSC speed), or use external-keyboard Ctrl+C.

8. Functions you can rely on

ABS(N) returns absolute value; ABS(-32768) overflows. INT(N) returns the same integer. SGN(N) returns -1, 0 or 1. RND(N) requires N from 1 to 32767 and returns 0 through N-1. The ROM's deterministic 16-bit generator starts from seed ACE1 when values reset. RUN repeats that initial sequence; there is no host-random number dependency or RANDOMIZE statement. Use RND(6)+1 for values 1–6.

ASC(S$) returns the first byte of a nonempty string. ASC("A") is 65, ASC("0") is 48 and ASC(" ") is 32. ASC("") raises BAD ARGUMENT. CHR$(N) creates one byte for N=0–255, including zero. Every value in that domain round-trips through ASC(CHR$(N)). A valid byte is not necessarily a visible glyph; reserved button bytes and control bytes are data, not printable ASCII. CHR$ does not discover hardware key codes.

LEN counts string bytes, including embedded NUL. LEFT$/RIGHT$ take a nonnegative count and clamp it to available bytes. MID$ uses a positive one-based start and optional nonnegative count; omitted count means the rest. A start past the end returns empty. Negative counts or start zero raise BAD ARGUMENT.

STR$ produces ordinary signed decimal without a leading space for positive numbers. VAL accepts a whole signed decimal with optional surrounding spaces. VAL("12X"), VAL("") and embedded NUL are invalid; out-of-range values overflow. These are not floating-point conversion routines. Function arguments retain their types; LEN(42), for example, raises TYPE MISMATCH.

INKEY$ has no parentheses. It returns one queued byte or an empty string immediately. It reads events while a program runs; a direct idle read normally returns empty. The controller-event table and focus rules are in Chapter 11. JOY(port) returns held-state masks and SPRCOL(a,b) returns a box-collision result; those numeric functions are described with sprites below and in the reference.

9. Graphics and the built-in sprite creator

SCREEN 0 is text. SCREEN 1 starts/clears a graphics canvas and its standard mapping. The canvas is 128×64 one-bit pixels, with local (0,0) at its top left and (127,63) at its bottom right. It occupies part of the NES screen, not a full-screen bitmap. COLOR selects one shared foreground/background pair. Valid NES palette indices are 0–63 except 13,29,45,61. The canvas does not have a separate color per pixel.

10 SCREEN 1
20 COLOR 42,15
30 RECT 8,8,119,55
40 LINE 0,0,127,63
50 PSET 64,32
60 END

PSET plots one pixel. LINE is an inclusive integer segment. RECT uses opposite corners, not width and height. An optional final ink argument of 0/1 clears/sets pixels. Points outside the canvas clip. FILL fills a four-connected region with a bounded worklist; a complicated region can report FILL TOO COMPLEX. Large operations paint progressively and remain interruptible.

TILE works on the NES nametable in SCREEN 1: column 0–31, row 0–29, pattern 0–255. Patterns are shared. A TILE referencing a canvas pattern changes when that pattern is drawn later. SCREEN 1 restores the standard mapping. CLS clears the active canvas; placements outside it remain. Text restoration clears the canvas.

Sprites are real 8×8 NES hardware sprites. SPRITE slot,x,y,art shows one of 64 slots, using x=0–255 and y=1–239. Art 0–7 is predefined: ship, player, enemy, ball, projectile, star, block, pointer. Art 8–39 is editable. MOVE changes a shown slot's position; HIDE hides it. SPRCOL(a,b) tests unclipped 8×8 bounding boxes of visible slots, including transparent pixels. It is not per-pixel collision. The ninth sprite on the same scanline is hidden by the hardware limit; no automatic flicker is added. Arrange sprites accordingly.

EDITSPR 8 opens BASIC's own creator, independent of Paint. D-pad moves/wraps on the grid, A paints and B erases. Select opens tools; choose color/art with the pad. Tools also clear, fill, mirror horizontally, flip vertically and undo. Start requests exit. If edited, choose KEEP, DISCARD or CANCEL. Kept art becomes available to SPRITE immediately; it is not permanent until you SAVE the project.

Each pattern has four indexed pixel values: 0 transparent, 1 green, 2 white, 3 blue. This is a shared fixed sprite palette, not arbitrary per-sprite color editing. There is no composed 16×16 editor or independently named sprite file. A named BASIC project stores all 32 kept 8×8 patterns. Reopen the art ID to edit it. After KEEP, use SCREEN 1:SPRITE 0,80,80,8 as a direct fragment to display art 8.

10. Sound and short melodies

BEEP plays a short note on pulse channel one. SOUND channel,pitch,duration starts or replaces a voice asynchronously. Channels 1/2 are pulse, 3 triangle, 4 noise. Tonal notes are integers 33–96 using MIDI note numbering as a convention: 60 is C4, 64 E4, 67 G4 and 69 A4. No MIDI device is required. Noise pitch is a hardware period index 0–15 rather than a musical note.

Duration is 0–32767 emulated frames. Zero mutes that voice, but its channel and pitch must still be valid. SOUND followed by WAIT makes notes sequential. Other BASIC statements add their own frame cost, so this is a simple sequencer, not an exact wall-clock audio workstation. The target is NTSC; PAL retuning is not part of this language edition.

10 SOUND 1,60,20
20 WAIT 20
30 SOUND 1,64,20
40 WAIT 20
50 SOUND 1,67,30
60 WAIT 30
70 END

This plays three notes and ends after their waits. Separate channels can form a chord. Voices have fixed amplitudes; there is no volume argument, music-string language or DMC/sample playback API. Normal source completion lets finite tones finish; END/STOP, errors, break, NEW/RUN and sprite-editor entry silence them. Pausing freezes emulation and can preserve a remaining note until resume.

In the browser, select Sound off in the playground toolbar to enable audio after a user gesture. Check device volume and the output route. In the iOS app, also check silent mode and VIDEO / AUDIO settings. Changing an audio route can pause the app.

11. Controllers, input events and a game loop

JOY(1) samples held virtual NES buttons. The mask is A=1, B=2, Select=4, Start=8, Up=16, Down=32, Left=64, Right=128. Simultaneous buttons add. Read once into J if several tests should use the same sample. There is no bitwise AND, but integer arithmetic extracts a bit: J/128 is Right; J/16-J/32*2 is Up.

INKEY$ instead queues new press edges on port one. Codes are A=128, B=129, Select=130, Start=131, Up=132, Down=133, Left=134, Right=135. They are reserved codes, not ASCII. Held gameplay buttons do not repeat each frame. Simultaneous edges queue in that order. Eight events fit; overflow drops the newest and increments a saturating internal counter. RUN/focus/input transitions clear the queue; the Start that launches RUN is not also an input event.

10 K$=INKEY$
20 IF K$="" THEN GOTO 10
30 PRINT "CODE=";ASC(K$)
40 GOTO 10

Press A while it runs: CODE=128 appears. An idle empty result loops before ASC, avoiding ASC(""). External keyboard text during RUN queues text bytes; it does not discover arbitrary USB/Bluetooth scan codes. The host or adapter maps a physical device to virtual NES buttons. Compatibility depends on that mapping.

Hold Select alone for 30 frames during RUN to open text keys. D-pad navigation then selects text rather than sending game-direction events. A sends the chosen character, B sends byte 8, Start sends byte 13, Select closes the keys. Short Select remains event 130. Start+Select is reserved for the emergency break. INPUT owns a separate edited-answer workflow, so do not expect it to consume these queued game events. After external-keyboard handshake, JOY(2) is zero.

10 SCREEN 1:X=80
20 SPRITE 0,X,100,0
30 J=JOY(1)
40 X=80+J/128*8
50 MOVE 0,X,100
60 WAIT 1:GOTO 30

Hold Right: the ship moves from X=80 to X=88. Release Right: it returns to 80. This small complete game loop demonstrates sampling, changing state, MOVE and WAIT without leaving the valid coordinate range. It does not implement continuous acceleration. You can replace art 0 with an art ID you created, then save the modified source and artwork. Chapter 13 suggests safe extensions.

12. Save and load without losing work

BASIC has six named project slots. SAVE "NAME" stores source and all 512 bytes of kept editable artwork; it does not store variable values, the canvas, active sound or execution position. Names contain 1–12 uppercase letters/digits or underscore, hyphen and period. SAVE or LOAD without a name uses PROGRAM. Wait for the success notice before leaving the cartridge.

SAVE asks before overwriting an existing name. LOAD asks before discarding dirty working code/art. A/Y/Enter accepts; B/N/Select/Escape cancels. FILES and CAT list the library. KILL "NAME" or ERASE "NAME" deletes after confirmation; KILL 1 (or ERASE 1) can explicitly remove a numbered slot, including an unreadable record. A full directory reports SAVE DIRECTORY FULL; overwrite intentionally or erase a file you no longer need. Slots are not automatically reclaimed from corruption.

LOAD validates a saved record before replacing working source/art. An intact name with damaged metadata/payload reports BAD SAVED PROJECT. A damaged name can produce FILE NOT FOUND instead. Do not repeatedly overwrite your only backup while troubleshooting. A checksummed native old-record journal recovers interrupted writes at boot or the next storage command when that backup is valid. It cannot repair arbitrary electrical loss or a corrupted backup.

New records are version 4; this ROM reads versions 2, 3 and 4 without silently rewriting older files. Older ROMs reject version-4 records before interpreting their tokens. Array contents are runtime values, excluded from ordinary SAVE. The browser preserves an earlier exact-ROM recovery and copies supported V1.0 source, artwork and native saves into a separately validated V1.1 session. Runtime values restart; the original recovery can be downloaded. Arbitrary ROM snapshots are not interchangeable. Keep original ROM/save files when archiving work.

The host's SAVE STATES is a separate emulator feature: snapshots belong to an exact ROM hash, core version and region. BASIC has no automatic-resume promise; use its explicit project commands. Loading an emulator snapshot keeps current committed cartridge files, rather than rolling those files back. These two forms of saving solve different problems.

On a physical board, SAVE requires compatible MMC1/SXROM banking and retained 32 KiB PRG SRAM, plus 8 KiB writable CHR RAM. A normal ROM chip alone cannot save; an 8 KiB SNROM board is insufficient. Emulator battery-file restart tests are verified, but physical NES, flashcart model, PCB/programmer and power-removal retention tests remain NOT VERIFIED.

13. Three complete projects to make your own

Project 1 is the name greeter in Chapter 5. Type its exact five lines and RUN. Try both NES USER and an empty answer. N$ holds input, A$ holds the greeting, + joins text, and the final IF notices empty input. Add a second independent numeric variable and PRINT it; never assign a number directly to A$. Save the finished version as GREETER. After a cold start, LOAD "GREETER" and RUN.

Project 2 is the sum in Chapter 7. Its output TOTAL=15 is an easy check of the loop. Change the limit from 5 to 10 and reason about the result before running. Try a descending loop with a negative STEP. Keep arithmetic within -32768…32767. A REM comment on a separate line can explain which variable is the running total. Save a working version as SUM before experimenting further.

Project 3 is the ship controller in Chapter 11. Its expected positions are 80 and 88. Draw art 8 in EDITSPR, KEEP it, then change line 20's art argument from 0 to 8. Save the project as SHIP. Load it after reset to check source and artwork together. Keep MOVE coordinates in range if you extend it. For smooth motion, add separate held-bit tests and explicit bounds before updating X; the original simple listing deliberately avoids accidental coordinate overflow.

The frame/diagonal and melody listings are additional complete samples. The input code diagnostic is a useful tool when you change controller mappings. All nine complete listings in this book have matching .bas source fixtures and executed ROM evidence. Short code fragments in prose/reference illustrate syntax and are not claimed to be standalone numbered programs.

14. Alphabetical command and function reference

Notation: N is a numeric expression; S$ a string expression; A a numeric variable; A$ a string variable; brackets mean an optional part and are not typed. Statements have no expression return value. A line target is a literal line number. A source line can contain colon-separated statements unless a command is direct-only. Functions return a typed value and are used inside expressions. THEN/TO/STEP are syntax fragments used by their parent statements. The reference covers all 61 V1.1 keyword tokens; it does not borrow commands from another BASIC dialect.

ABS

Syntax: ABS(N)

Parameters: N: signed integer.

Result: integer.

Example fragment: PRINT ABS(-5)

Absolute value; -32768 has no positive signed 16-bit representation.

Errors: OVERFLOW (9); TYPE MISMATCH (25).

ASC

Syntax: ASC(S$)

Parameters: S$: nonempty string.

Result: integer.

Example fragment: PRINT ASC("A")

First unsigned byte,0–255; does not inspect arbitrary device scan codes.

Errors: BAD ARGUMENT (11) for empty; TYPE MISMATCH (25).

BEEP

Syntax: BEEP

Parameters: No arguments.

Result: statement; no value.

Example fragment: BEEP

Starts/replaces pulse 1 note 69 for 12 emulated frames. Other voices remain.

Errors: SYNTAX ERROR (1) for arguments.

CAT

Syntax: CAT

Parameters: No arguments; direct command.

Result: statement; no value.

Example fragment: CAT

Alias for FILES. Lists six project slots; does not LOAD a project.

Errors: SYNTAX ERROR (1); DIRECT COMMAND ONLY (6).

CHR$

Syntax: CHR$(N)

Parameters: N: integer 0–255.

Result: string.

Example fragment: A$=CHR$(72)+CHR$(73)

Creates exactly one byte, including NUL. A supported byte need not be a printable glyph.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25); STRING SPACE FULL (26).

CLEAR

Syntax: CLEAR

Parameters: No arguments.

Result: statement; no value.

Example fragment: CLEAR

Resets numeric/string values, releases all numeric arrays, resets control frames and random seed; stops sound/hides sprites. Keeps source and kept artwork.

Errors: SYNTAX ERROR (1).

CLS

Syntax: CLS

Parameters: No arguments.

Result: statement; no value.

Example fragment: CLS

Clears terminal in text mode, canvas in graphics. Does not remove saved source or all hardware sprites.

Errors: SYNTAX ERROR (1).

COLOR

Syntax: COLOR foreground,background

Parameters: Two numeric NES palette indices 0–63, excluding 13/29/45/61.

Result: statement; no value.

Example fragment: COLOR 42,15

One shared foreground/background pair. Text may also use it; sprite palette remains fixed.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

DEMOS

Syntax: DEMOS

Parameters: No arguments; direct command.

Result: statement; no value.

Example fragment: DEMOS

Lists six editable built-in examples. Does not use saved-file slots.

Errors: SYNTAX ERROR (1); DIRECT COMMAND ONLY (6).

DIM

Syntax: DIM A(upper) or DIM B(upper1,upper2)

Parameters: One-letter numeric array and nonnegative integer upper bounds.

Result: Allocates zero-filled signed 16-bit cells; no expression value.

Example fragment: DIM B(9,19):B(4,19)=7:PRINT B(4,19)

Zero-based, inclusive bounds. All 26 arrays share 1,216 elements. Scalars and strings use independent names. One declaration per statement. Repeated DIM is an error. RUN/CLEAR/NEW/LOAD/LOADDEMO/reset release arrays. SAVE keeps source/art, not live contents. See Chapter 4 for the complete board program.

Errors: TYPE MISMATCH (25); ARRAY ALREADY DIMENSIONED (29); ARRAY SPACE FULL (31); BAD ARRAY DIMENSION (32); syntax/number/expression errors. Indexed reads/writes may also raise ARRAY NOT DIMENSIONED (28) or SUBSCRIPT OUT OF RANGE (30).

EDITSPR

Syntax: EDITSPR art

Parameters: Numeric art ID 8–39; whole direct command.

Result: statement; no value.

Example fragment: EDITSPR 8

32 native 8×8 two-bit patterns. Keep/discard/cancel; KEEP is session-only until project SAVE. No colon continuation.

Errors: BAD ARGUMENT (11); DIRECT COMMAND ONLY (6); SYNTAX ERROR (1).

END

Syntax: END

Parameters: No arguments.

Result: statement; no value.

Example fragment: 30 END

Finishes execution, clears pending control frames and stops sound. Keeps source and final scene.

Errors: SYNTAX ERROR (1).

ERASE

Syntax: ERASE ["NAME" | slot]

Parameters: Direct command; name rules match SAVE, slot 1–6.

Result: statement; no value.

Example fragment: ERASE "DEMO"

Confirmed deletion, alias of KILL; cancel retains the file. Without a name uses PROGRAM.

Errors: FILE NOT FOUND (22); BAD ARGUMENT (11); DIRECT COMMAND ONLY (6).

FILES

Syntax: FILES

Parameters: No arguments; direct command.

Result: statement; no value.

Example fragment: FILES

Lists the six-slot directory, including available/damaged entries. Does not clear working code.

Errors: SYNTAX ERROR (1); DIRECT COMMAND ONLY (6).

FILL

Syntax: FILL x,y[,ink]

Parameters: Numeric seed in local canvas coordinates; ink 0/1, default 1.

Result: statement; no value.

Example fragment: FILL 20,20

SCREEN 1 required. Four-connected bounded flood fill; clipped/already-matching seed is a no-op.

Errors: FILL TOO COMPLEX (21); GRAPHICS MODE REQUIRED (20); BAD ARGUMENT (11); TYPE MISMATCH (25).

FOR

Syntax: FOR A=start TO limit [STEP step]

Parameters: Numeric single-letter variable; numeric expressions; nonzero step, default 1.

Result: statement; no value.

Example fragment: 10 FOR I=1 TO 5

Program loop, inclusive limit; negative/zero-trip loops supported. Shares eight-frame stack with GOSUB.

Errors: BAD ARGUMENT (11) for zero step; CONTROL STACK FULL (18); LOOP VARIABLE IN USE (19); PROGRAM ONLY (16).

GOSUB

Syntax: GOSUB line

Parameters: Literal existing line 1–65535; program statement.

Result: statement; no value.

Example fragment: 10 GOSUB 100

Saves current source location for RETURN, including a colon continuation. Shares eight control frames.

Errors: UNDEFINED LINE (12); CONTROL STACK FULL (18); PROGRAM ONLY (16); BAD LINE NUMBER (3).

GOTO

Syntax: GOTO line

Parameters: Literal existing line 1–65535; program statement.

Result: statement; no value.

Example fragment: 20 GOTO 10

Jumps without saving a return location. A variable/expression is not a line-target substitute.

Errors: UNDEFINED LINE (12); PROGRAM ONLY (16); BAD LINE NUMBER (3).

HELP

Syntax: HELP [page]

Parameters: Direct command; literal page 1–10; omitted means 1.

Result: statement; no value.

Example fragment: HELP 8

Native text reference: strings/input 7, input codes 8, functions/editing 9. It does not open this host PDF.

Errors: BAD ARGUMENT (11); DIRECT COMMAND ONLY (6); SYNTAX ERROR (1).

HIDE

Syntax: HIDE slot

Parameters: Numeric sprite slot 0–63.

Result: statement; no value.

Example fragment: HIDE 0

Safe for an already-hidden slot; permitted in either text or graphics mode.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

IF

Syntax: IF condition THEN line-or-statement

Parameters: Numeric condition; string comparisons produce numeric truth. Program statement.

Result: statement; no value.

Example fragment: 10 IF N$="" THEN PRINT "EMPTY"

Nonzero is true. A false condition skips the rest of its whole line. Inline THEN and literal targets supported; no ELSE.

Errors: PROGRAM ONLY (16); UNDEFINED LINE (12); TYPE MISMATCH (25); syntax/range errors in expressions.

INKEY$

Syntax: INKEY$

Parameters: No arguments or parentheses.

Result: string.

Example fragment: K$=INKEY$

Nonblocking one queued event byte or empty string. In RUN, reserved button edge codes 128–135. Eight-event ring; drop newest on overflow.

Errors: STRING SPACE FULL (26) on temporary exhaustion. Empty is normal; ASC(empty) is not.

INPUT

Syntax: INPUT [prompt;]A, INPUT [prompt;]A$, or INPUT [prompt;]A(index[,index])

Parameters: Optional string prompt; one numeric/string variable or numeric array cell. Cell indexes are evaluated once, before prompting.

Result: statement; no value.

Example fragment: INPUT "NAME";N$

Uses 95-character line editor. Empty strings valid; numeric empty/invalid retries. String limit 63/shared pool applies.

Errors: BAD INPUT (17); STRING TOO LONG (27); STRING SPACE FULL (26); BREAK (8); TYPE MISMATCH (25).

INT

Syntax: INT(N)

Parameters: N: integer.

Result: integer.

Example fragment: PRINT INT(-7)

Identity in an integer-only language; does not enable fractional literals or floating point.

Errors: TYPE MISMATCH (25); expression syntax/range errors.

JOY

Syntax: JOY(port)

Parameters: Numeric port 1 or 2.

Result: integer.

Example fragment: J=JOY(1)

Held-button sum:1/2/4/8/16/32/64/128. Port 2 returns 0 after optional external-keyboard handshake, until reset.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

KILL

Syntax: KILL ["NAME" | slot]

Parameters: Direct command; name rules match SAVE, slot 1–6.

Result: statement; no value.

Example fragment: KILL 1

Confirmed deletion, alias of ERASE. Numbered slot can explicitly delete a damaged entry. No automatic reclamation.

Errors: FILE NOT FOUND (22); BAD ARGUMENT (11); DIRECT COMMAND ONLY (6).

LEFT$

Syntax: LEFT$(S$,N)

Parameters: String and nonnegative numeric count.

Result: string.

Example fragment: A$=LEFT$("HELLO",2)

Returns up to N bytes from the start. Zero is empty; oversized count clamps to string length.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25); destination/temporary string limits 26/27.

LEN

Syntax: LEN(S$)

Parameters: String expression.

Result: integer.

Example fragment: A=LEN("HELLO")

Counts bytes, including embedded NUL. Stored variables max 63, but a literal can use the line limit.

Errors: TYPE MISMATCH (25); expression errors.

LET

Syntax: LET variable=expression

Parameters: A–Z numeric or A$–Z$ string variable with matching typed expression.

Result: statement; no value.

Example fragment: LET A$="HELLO"

LET is optional. Independent numeric/string variables and numeric arrays; no long identifiers or implicit conversion. Indexed assignment uses the same checked numeric expressions.

Errors: TYPE MISMATCH (25); STRING SPACE FULL (26); STRING TOO LONG (27); expression errors.

LINE

Syntax: LINE x1,y1,x2,y2[,ink]

Parameters: Signed numeric endpoints, optional ink 0/1 default 1.

Result: statement; no value.

Example fragment: LINE 0,0,127,63

SCREEN 1; inclusive integer Bresenham line, each point clips to 128×64 canvas. Very long segments can take many frames.

Errors: GRAPHICS MODE REQUIRED (20); BAD ARGUMENT (11); TYPE MISMATCH (25).

LIST

Syntax: LIST

Parameters: No arguments; direct command.

Result: statement; no value.

Example fragment: LIST

Displays tokenized source in numeric order. Long output pages: Start continues, Select cancels.

Errors: DIRECT COMMAND ONLY (6); BREAK (8); BAD PROGRAM (7) if source is invalid.

LOAD

Syntax: LOAD ["NAME"]

Parameters: Direct command; quoted 1–12-character name or default PROGRAM.

Result: statement; no value.

Example fragment: LOAD "HELLO"

Validates source/art before replacement; confirms dirty working data. Clears values, restores saved art. Read versions 2/3/4.

Errors: FILE NOT FOUND (22); BAD SAVED PROJECT (23); DIRECT COMMAND ONLY (6); BREAK (8).

LOADDEMO

Syntax: LOADDEMO number

Parameters: Literal built-in demo 1–6; direct command.

Result: statement; no value.

Example fragment: LOADDEMO 6

Replaces working source after confirmation if dirty. Retains kept artwork, uses no save slot. Demo 6 is input diagnostic.

Errors: BAD ARGUMENT (11); DIRECT COMMAND ONLY (6); BREAK (8).

LOCATE

Syntax: LOCATE column,row

Parameters: Numeric column 0–27, row 0–21.

Result: statement; no value.

Example fragment: LOCATE 4,3

Sets text output position. Restores text if currently in graphics; graphics surface is cleared in that transition.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

MEM

Syntax: MEM

Parameters: None; available directly or in a numbered program.

Result: Prints V1.1 and remaining tokenized code bytes, line records, array elements, and string-pool bytes. Use FILES for save directory usage.

Example fragment: DIM A(9):MEM

The new array consumes ten cells, leaving 1,206. MEM does not release arrays or reset values. Its text output returns to text mode, like PRINT.

Errors: SYNTAX ERROR (1) for arguments.

MID$

Syntax: MID$(S$,start[,count])

Parameters: String, numeric positive one-based start, optional nonnegative count.

Result: string.

Example fragment: A$=MID$("HELLO",2,3)

Count defaults to rest. Past end returns empty; count clamps to available bytes.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25); string destination/temporary limits 26/27.

MOVE

Syntax: MOVE slot,x,y

Parameters: Numeric visible slot 0–63, x 0–255, y 1–239.

Result: statement; no value.

Example fragment: MOVE 0,88,100

SCREEN 1 required; preserves slot artwork. A hidden slot is an invalid MOVE target.

Errors: BAD ARGUMENT (11); GRAPHICS MODE REQUIRED (20); TYPE MISMATCH (25).

NEW

Syntax: NEW

Parameters: No arguments; direct command.

Result: statement; no value.

Example fragment: NEW

Confirms nonempty dirty source; resets program/values, stops sound/hides sprites. Keeps kept artwork. Does not erase saved files.

Errors: DIRECT COMMAND ONLY (6); SYNTAX ERROR (1).

NEXT

Syntax: NEXT A

Parameters: Numeric variable used by the active FOR.

Result: statement; no value.

Example fragment: 40 NEXT I

Advances by STEP and loops or finishes. Active frame must match; variable remains at its post-loop value.

Errors: UNMATCHED LOOP (14); OVERFLOW (9); PROGRAM ONLY (16); TYPE MISMATCH (25).

PRINT

Syntax: PRINT [expression[;|,expression]...]

Parameters: Numeric/string expressions; optional trailing separator.

Result: statement; no value.

Example fragment: PRINT "VALUE=";A

Semicolon joins, comma uses four-column tab stops. Default ends line; trailing separator preserves position. Restores text from graphics.

Errors: OUTPUT TOO LONG (5); TYPE MISMATCH (25); expression errors; BREAK (8) on canceled pages.

PSET

Syntax: PSET x,y[,ink]

Parameters: Signed numeric local coordinates, optional ink 0/1 default 1.

Result: statement; no value.

Example fragment: PSET 64,32

SCREEN 1; set/clear a point in 128×64 canvas. Out-of-canvas coordinates clip to no-op.

Errors: GRAPHICS MODE REQUIRED (20); BAD ARGUMENT (11); TYPE MISMATCH (25).

RECT

Syntax: RECT x1,y1,x2,y2[,ink]

Parameters: Numeric opposite corners, optional ink 0/1 default 1.

Result: statement; no value.

Example fragment: RECT 8,8,119,55

SCREEN 1; outline, not filled rectangle or x/y/width/height. Reversed and degenerate corners supported; clipping applies.

Errors: GRAPHICS MODE REQUIRED (20); BAD ARGUMENT (11); TYPE MISMATCH (25).

REM

Syntax: REM comment

Parameters: Remaining characters on the source line.

Result: statement; no value.

Example fragment: 10 REM A IS THE RUNNING TOTAL

Comment consumes the rest of the line, including colon/keywords. It is not an executable statement separator.

Errors: Physical/source memory bounds still apply.

RETURN

Syntax: RETURN

Parameters: No arguments; matching GOSUB frame.

Result: statement; no value.

Example fragment: 110 RETURN

Resumes the saved source/colon continuation. Natural source EOF with pending GOSUB also reports an invalid return.

Errors: INVALID RETURN (13); PROGRAM ONLY (16).

RIGHT$

Syntax: RIGHT$(S$,N)

Parameters: String and nonnegative numeric count.

Result: string.

Example fragment: A$=RIGHT$("HELLO",2)

Returns up to N bytes from end. Zero returns empty; oversized count clamps to available bytes.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25); string destination/temporary limits 26/27.

RND

Syntax: RND(N)

Parameters: Numeric N 1–32767.

Result: integer.

Example fragment: A=RND(6)+1

Returns 0 through N-1 using deterministic 16-bit LFSR. Variable reset seeds ACE 1; RUN repeats initial sequence. No RANDOMIZE.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

RUN

Syntax: RUN ["NAME"]

Parameters: Whole direct command; optional quoted saved name.

Result: statement; no value.

Example fragment: RUN "HELLO"

Starts from beginning with reset values. Named form validates/loads source/art and confirms dirty replacement. Does not SAVE.

Errors: FILE NOT FOUND (22); BAD SAVED PROJECT (23); DIRECT COMMAND ONLY (6); runtime errors from program.

SAVE

Syntax: SAVE ["NAME"]

Parameters: Whole direct command; optional quoted name, default PROGRAM.

Result: statement; no value.

Example fragment: SAVE "HELLO"

Six slots, names 1–12 uppercase letters/digits/_/./-. Source and kept art only. Confirm overwrite; wait for SAVED notice. Writes version 4. Reads version 2/3/4 projects without changing the originals. Older ROMs reject version 4. Array values are not stored.

Errors: SAVE DIRECTORY FULL (24); BAD PROGRAM (7); DIRECT COMMAND ONLY (6); BREAK (8).

SCREEN

Syntax: SCREEN mode

Parameters: Numeric 0=text,1=graphics.

Result: statement; no value.

Example fragment: SCREEN 1

Graphics start clears canvas/restores tile mapping/default colors. Return to text clears canvas. Hides sprites during screen transition.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

SGN

Syntax: SGN(N)

Parameters: Numeric expression.

Result: integer.

Example fragment: A=SGN(-42)

Returns -1 for negative,0 for zero,1 for positive. No floating-point conversion.

Errors: TYPE MISMATCH (25); expression errors.

SOUND

Syntax: SOUND channel,pitch,duration

Parameters: Numeric channel 1–4; tonal notes 33–96 for 1–3, noise index 0–15 for 4; duration 0–32767 frames.

Result: statement; no value.

Example fragment: SOUND 1,69,60

Asynchronous, replaces selected voice; duration 0 mutes it. Fixed levels; no DMC/samples. NTSC pitch target.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

SPRCOL

Syntax: SPRCOL(a,b)

Parameters: Numeric sprite slots 0–63.

Result: integer.

Example fragment: A=SPRCOL(0,1)

1 when both visible unclipped 8×8 boxes overlap,0 otherwise. Touching edges do not overlap; transparent pixels still count.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25).

SPRITE

Syntax: SPRITE slot,x,y,art

Parameters: Numeric slot 0–63, x 0–255, y 1–239, art 0–39.

Result: statement; no value.

Example fragment: SPRITE 0,80,100,0

SCREEN 1 required. Native 8×8 hardware sprite; art 0–7 predefined,8–39 kept editable. Eight per scanline.

Errors: BAD ARGUMENT (11); GRAPHICS MODE REQUIRED (20); TYPE MISMATCH (25).

STEP

Syntax: FOR A=start TO limit STEP step

Parameters: Numeric nonzero step in FOR syntax.

Result: grammar fragment.

Example fragment: 10 FOR I=5 TO 1 STEP -1

FOR grammar fragment, not a standalone command. Default step is 1; negative steps supported.

Errors: BAD ARGUMENT (11) for zero step; FOR/control errors.

STOP

Syntax: STOP

Parameters: No arguments.

Result: statement; no value.

Example fragment: 50 STOP

Intentional program termination with control-frame cleanup and sound stop, like END; no CONT command is supplied.

Errors: SYNTAX ERROR (1).

STR$

Syntax: STR$(N)

Parameters: Signed integer expression.

Result: string.

Example fragment: A$=STR$(-42)

Decimal text, minus sign for negatives, no positive leading space. Does not enable decimal fractions.

Errors: TYPE MISMATCH (25); STRING SPACE FULL (26); expression errors.

THEN

Syntax: IF condition THEN line-or-statement

Parameters: Part of IF grammar.

Result: grammar fragment.

Example fragment: 10 IF A=1 THEN PRINT "YES"

Not a standalone command. Literal target or inline statement; false skips whole remainder of line. No ELSE.

Errors: IF/program/target/expression errors.

TILE

Syntax: TILE column,row,id

Parameters: Numeric column 0–31, row 0–29, pattern 0–255.

Result: statement; no value.

Example fragment: TILE 0,0,65

SCREEN 1 native nametable placement, no palette argument. Patterns share; drawing changes referenced canvas patterns.

Errors: BAD ARGUMENT (11); GRAPHICS MODE REQUIRED (20); TYPE MISMATCH (25).

TO

Syntax: FOR A=start TO limit [STEP step]

Parameters: Numeric inclusive limit within FOR.

Result: grammar fragment.

Example fragment: 10 FOR I=1 TO 5

FOR grammar fragment, not a standalone command. Initial value past limit can yield zero trips.

Errors: FOR/program/expression errors.

VAL

Syntax: VAL(S$)

Parameters: String containing whole signed decimal with optional surrounding spaces.

Result: integer.

Example fragment: A=VAL(" -42 ")

Strict parse, not prefix conversion. Empty, trailing garbage and embedded NUL invalid; range -32768…32767.

Errors: BAD ARGUMENT (11); OVERFLOW (9); TYPE MISMATCH (25).

WAIT

Syntax: WAIT frames

Parameters: Numeric 0–32767 emulated frames.

Result: statement; no value.

Example fragment: WAIT 60

Yields interruptibly; zero adds no delay. Counts emulated time, freezes on app pause. Other statements add their own time.

Errors: BAD ARGUMENT (11); TYPE MISMATCH (25); BREAK (8).

15. Errors, recovery and troubleshooting

Read the exact message first. During RUN the suffix IN line identifies the source line. Return to editing, correct that numbered line, and RUN again. Failed line storage keeps the previous valid record. Failed typed assignment keeps its old destination. Reset is not the first repair step: it discards unsaved work.

SYNTAX ERROR often means missing quotes, a parenthesis/comma, extra punctuation, a wrong keyword or an unsupported identifier. BAD NUMBER is a literal outside the numeric domain; OVERFLOW is arithmetic/conversion beyond the checked range. TYPE MISMATCH needs an explicit STR$/VAL conversion or a corrected variable type. BAD INPUT retries an edited numeric answer. A bad string INPUT can retry after STRING TOO LONG or STRING SPACE FULL. Empty strings are valid input but not valid arguments to ASC or VAL.

UNDEFINED LINE means a GOTO/GOSUB/THEN target does not exist. INVALID RETURN means there is no matching GOSUB, or source ended while one was pending. UNMATCHED LOOP means FOR/NEXT frames do not match, including missing NEXT. LOOP VARIABLE IN USE means a nested FOR reuses an active numeric loop variable. CONTROL STACK FULL or EXPRESSION TOO DEEP calls for simpler nesting, not a larger host heap.

GRAPHICS MODE REQUIRED needs SCREEN 1 before drawing/SPRITE/MOVE. BAD ARGUMENT usually signals a range, count, mode parameter or invalid hidden-slot MOVE. FILL TOO COMPLEX is the bounded seed worklist, not a host crash. FILE NOT FOUND, BAD SAVED PROJECT and SAVE DIRECTORY FULL need the file checks in Chapter 12. BREAK is the expected result of an interruption or canceled output page.

If a controller seems stuck, release it, check whether the on-screen keyboard has focus, and use the app PAUSE control. A disconnected gamepad pauses the app. Text typing belongs to BASIC only while that ROM is running. Opening this host guide pauses and isolates input; close it and explicitly Resume to continue. A PDF view failure does not imply that the NES ROM is corrupt; use Help's safe Back/Close action and its local export option if available.

16. Appendices: codes, limits and edition history

Printable text follows ASCII where the font/editor support it: space 32, quotation mark 34, digits 48–57, uppercase letters 65–90. Keyboard source entry normalizes lowercase to uppercase. CHR$ can create all bytes 0–255, but unsupported or control glyphs are not promised visible. LEN counts bytes, not Unicode characters.

The relevant control bytes are Backspace 8, Enter 13, Escape 27 and the optional bridge's caret controls 28–31. Ctrl+C is byte 3 and always interrupts rather than becoming an ordinary queued text event. The reserved controller-event table is:

Supported: integer math, typed strings, the reference's functions, native input and controller events, text I/O, line/branch/loop/subroutine control, one-bit canvas, hardware sprites/editor, asynchronous APU sound and explicit project storage and numeric arrays. Unsupported: long variable names, string arrays, floats, ELSE, DATA/READ, ON GOTO, arbitrary gamepad scan codes, Unicode source, arbitrary sprite palettes, composed-sprite editing or inter-ROM project transfer. Future features are not promised by this edition.

Edition 1.1 extends the browser ROM with DIM, numeric arrays and MEM. Existing keyword values 128–186 are unchanged; DIM is 187 and MEM is 188. New saves use version 4 to make old interpreters reject them safely. The six 4 KiB slots, 64-byte headers, 3,072-byte source area, 512-byte artwork and transactional journal retain their boundaries. V1.1 reads version 2/3 projects without rewriting them. Array workspace uses the six previously unused 448-byte slot tails, outside committed records and their CRC. Array memory is volatile language state despite occupying battery-backed RAM. Boot/RUN reset descriptors; DIM zeroes its cells. The standalone ROM still uses NES 2.0, mapper 1/submapper 0, 128 KiB PRG ROM, 8 KiB CHR RAM and 32 KiB PRG NVRAM, NTSC.

Physical NES/flashcart acceptance remains NOT VERIFIED. Windows/macOS PDF readers can open an exported copy of the book; that does not imply a separate native 8-Bit Impostor app exists on those platforms. The app's actual supported build is iOS/iPadOS 17 or later. iOS-app compatibility on Mac is not certified here.

See ABOUT → SOFTWARE NOTICES in the app for project/core/font licenses. No public product-support URL or email was confirmed for this edition; none is invented in this book. Original NDB software is independent of Nintendo. Use only ROMs you have rights to use. The guide's pixel artwork is original, and the embedded reading/code fonts retain their redistribution licenses with the build source.