A port of Enhanced 68k BASIC (originally for EASy68k simulator) to the Motorola MVME167-02 single-board computer with 167-Bug ROM monitor.

This is a working implementation of Lee Davison's Enhanced 6800 BASIC interpreter, adapted to run on real 68040 hardware. The interpreter runs entirely in RAM and uses the 167-Bug TRAP #15 interface for I/O.

• Motorola MVME167-02 (or compatible) single-board computer
• 68040 CPU (or 68030/68020 with modifications)
• 167-Bug ROM monitor firmware
• Serial terminal connection

• Code Load Address: 0x00401000
• Program Storage: 0x00500000 - 0x01FFFFFF (32MB BASIC program space)
• Stack: 0x00500000 (grows downward from program start)

• vasmm68k_mot assembler (vasm for Motorola syntax)
• Standard Unix tools (make, rm, mkdir)

make              # Build S-record file
make clean        # Remove build artifacts

Output: build/enhanced_basic_ram.srec

1. Connect to MVME167 via serial terminal
2. Enter 167-Bug monitor
3. Load the S-record:

   167-Bug> lo 0
   [Paste contents of build/enhanced_basic_ram.srec]
   

4. Start BASIC:

   167-Bug> go 401000
   

• ✅ Interactive command line with prompt
• ✅ Line entry and editing
• ✅ LIST - Display program
• ✅ RUN - Execute program
• ✅ NEW - Clear program
• ✅ PRINT - Output text and variables
• ✅ FOR/NEXT loops (including nested loops)
• ✅ IF/THEN conditionals
• ✅ GOTO and GOSUB/RETURN
• ✅ DIM - Array declarations
• ✅ Array operations (single and multi-dimensional)
• ✅ Arithmetic operations (+, -, *, /)
• ✅ Comparison operators (=, <, >, <=, >=, <>)
• ✅ Variable assignments
• ✅ Ctrl-C to exit to 167-Bug

• ⚠️ TI (timer) function returns 0 (not yet implemented)
• ⚠️ INPUT statement untested
• ⚠️ String operations untested
• ⚠️ File I/O not implemented (simulator-only feature)
• ⚠️ Graphics commands not implemented

10 PRINT "HELLO WORLD"
RUN

10 FOR I = 1 TO 10
20   PRINT "COUNT: "; I
30 NEXT I
RUN

See Sieve.BAS for a complete benchmark program.

The interpreter uses 167-Bug's TRAP #15 interface:

• $0020 .OUTCHR - Output character (stack-based)
• $0000 .INCHR - Input character (stack-based)
• $0001 .INSTAT - Check input status
• $0063 .RETURN - Exit to 167-Bug

BASIC program lines are stored as:

[4-byte next pointer][2-byte line number][tokens...][0x00 terminator]

The 68040 is big-endian (MSB first). All multi-byte values are stored with the most significant byte at the lowest address.

• Ctrl-C Throttling: VEC_CC only checks for input every 64 BASIC statements to avoid TRAP storm
• Memory Alignment: Program storage forced to even addresses for 68040 compatibility

1. Line Numbers: Changed from 32-bit to 16-bit storage
2. I/O System: Replaced EASy68k TRAP #15 with 167-Bug TRAP #15
3. Memory Alignment: Added EVEN directives and runtime checks for 68040
4. GOTO Execution: Fixed execution flow to preserve FOR/NEXT stack
5. Big-Endian Support: Corrected byte ordering for line number storage/retrieval
6. Performance: Throttled Ctrl-C checking to prevent ROM monitor overload

• Fixed line number storage using wrong word in big-endian longword
• Fixed GOTO skipping incorrect number of bytes (was 2, needed 6)
• Fixed GOTO stack corruption when called from IF statement
• Fixed VEC_CC TRAP storm causing system crashes
• Fixed memory alignment issues causing odd-address faults

From Lee Davison's original documentation:

• Keywords must be in ALL UPPERCASE
• Variable names can be mixed case (first 3 letters determine uniqueness)
• RND(0) generates random numbers (not RND(1) like Microsoft BASIC)
• Arrays must be explicitly dimensioned with DIM
• Empty INPUT responses cause program break (by default)
• PRINT does not add spaces between items
• Undefined variables generate errors (by default)

• Original BASIC: Lee Davison's Enhanced 6800 BASIC
• EASy68k Port: Original EASy68k simulator version
• MVME167 Port: John (2024)
• AI Assistant: Claude (Anthropic) - debugging and optimization

EhBASIC is copyright Lee Davison 2002-2012 and free for educational or personal use only. For commercial use please contact the original author.

Contributions welcome! Areas needing work:

• Implement proper TI timer function using 167-Bug .TIME
• Test and fix INPUT statement
• Test string operations
• Optimize floating-point math routines
• Add graphics support (Tektronix 4010, Sixel, or ASCII art)

Current Status: Working for integer arithmetic, loops, arrays, and control flow

Last Updated: December 2024

1. EhBASIC Manual
2. Lee Davison's Website
3. EASy68k
4. VASM Assembler