Software component of the single board computer design using a M68000 CPU. Hardware designs can be found in the mcd-pcb repo.
- Save last loaded program start location, use with
GOwhen no arguments - Save list of user loaded programs
- Split into separate files with
INCLUDEpre-processor directive - Use hardware UART echo mode (loopback)
- Use UART interrupt mode instead of polling
- Memory management
Program memory Structure
| Address | Purpose |
|---|---|
| ROM | |
00_0000 |
Exception Vector table |
00_8000 |
Monitor program start |
00_88CA |
Command table start |
00_891E |
String Constant storage |
| RAM | |
01_0000 |
Program Data. Global variables & line buffer |
01_1000 |
Recommended user program locations |
01_FFF0 |
System Stack start. Fills up from bottom |
| DEVICE | |
02_000 |
Serial device start (odd addresses only) |
Many subroutines set flags in D7 to indicate error
| D7 Bit | Flag |
|---|---|
| 0 | invalid hex input |
| 1 | invalid hex parameter |
| 2 | S-Record checksum error |
Used to terminate programs running in user mode. Use like C's return from main() or exit().
System Calls available with TRAP #15
Put task number in D0.B
| Task | Usage |
|---|---|
| 0 | Print the byte in D1.B |
| 1 | Print the word in D1.W |
| 2 | Print Lowest 6 bytes in D1 |
| 3 | Print the longword in D1.L |
| 4 | Print newline |
| 5 | Read single ascii character into D1.B |
| 6 | Display single ascii character in D1.B |
| 7 | Read a hex character into D1. All input routines set D7 bit 0 (LSB) on conversion error |
| 8 | Read a hex byte into D1.B |
| 9 | Read a hex word into D1.W |
| 10 | Read a longword into D1.L |
| 11 | Toggle input upper case conversion. D1.B=0 (disable), !=0 (enable, default) |
| 12 | Toggle keyboard echo. D1.B=0 (disable), !=0 (enabled, default) |
| 13 | Display Null terminated string at A1 with trailing CR,LF |
| 14 | Display Null terminated string at A1 |
Clements, A. (1997) Microprocessor Systems Design: 68000 hardware, software, and interfacing. PWS Publishing Company.