The latest release of this Firmware is detailed in the table below.
| Name | Small Computer Monitor |
| Configuration | S6 |
| Release | 2022-02-27 |
| Download ROM image | SCM S6 2022-02-27 |
| Download source code | SCW 2022-03-01 |
| Device Programming: | |
| Code size | 32k bytes |
| Checksum (MiniPro 6.6) | 07D2 FD08 (SST39SF040) |
| Recommended IC | SST39SF040 |
| Core Components: | |
| Monitor | Version 1.3.0 |
| BIOS | SCZ180 1.3.0 |
| Included Apps: | |
| – ROM BASIC | Version 4.7b.1 |
| – CP/M loader from CF card | Version 1.0 |
The firmware is supplied (above) as an Intel HEX format file, which is suitable for use by most PROM programmers. Intel HEX files are a text format, not a binary format. As a result, they are larger than the stated code size in the table above.
The Small Computer Monitor’s Components and Apps are described here.
Source code can be found in the Small Computer Workshop download.
Diagnostic display
At reset, the 8 LEDs next to the power LED are used to display the results of the self-test diagnostics. Each LED should light for a fraction of a second and the test should end with all 8 LEDs being turned off. Failures are indicated as follows.
| Display | Issue |
| Light sequence repeats indefinitely | RAM test failed |
| LED bit 0 remains on | Serial port test failed |
| No light sequence | CPU not running, or output port failed |
Supported devices
- Z180 CPU (eg. Z8S180xx) at 18.432 MHz
- Z180’s asynchronous serial ports
- Z180’s timer (for idle events)
- SIO #1 at 0x80 (eg. Z84C4xxx) [rc addressing]
- SIO #1 at 0x80 (eg. Z84C4xxx) [zilog addressing]
- SIO #2 at 0x84 (eg. Z84C4xxx) [rc addressing]
- SIO #2 at 0x84 (eg. Z84C4xxx) [zilog addressing]
- CTC #1 at 0x88 (eg. Z84C30xx)
- CTC #2 at 0x8C (eg. Z84C30xx)
- ACIA #1 at 0x80 (eg. 68B50)
- ACIA #2 at 0x40 (eg. 68B50)
- CF Card at 0x10 for loading CP/M
- Diagnostic LEDs and digital I/O at 0x0D
The SIO can either use the RC2014 addressing scheme or the typical Zilog scheme (as used by Dr. S. Baker’s SIO module)
The addresses of the official RC2014 SIO and ACIA modules clash, so they can’t both be installed at the same time. Also, it needs a 7.3728 MHz clock source. Third-party modules often have address options and onboard clock sources to avoid these problems.
The official RC2014 SIO module does not have tight address decoding so it appears as an SIO at both 0x80 and 0x84. Also, it needs a 7.3728 MHz clock source.
The lack of specific support does not exclude the use of other hardware. It just means the ROM does not do anything specific with it.
Supported hardware
- Processor:
- SC126, Z180 Motherboard (Z180 CPU at 18.432 MHz)
- Memory:
- SC126, Z180 Motherboard (512k RAM, 512k ROM)
- Serial port:
- SC126, Z180 Motherboard (2 x ASCI ports)
- Karl’s #61, serial and storage (ACIA & CF)
- SC104, serial module (Z80 SIO/2)
- SC132, serial module (Z80 SIO/0) with 7.3728 osc.
- SC139, serial module (68B50 ACIA)
- and others
- Timer:
- SC126, Z180 Motherboard (16-bit counter/timer)
- SC102, counter timer module (Z80 CTC)
- Baud rate generation:
- SC126, Z180 Motherboard (150 to 115200 baud)
- Digital I/O:
- SC129, Digital I/O module (8 out, 8 in, all with LEDs)
- RC2014, digital I/O module (8 x LEDs, 8 x switches)
- CP/M storage:
- Self-test status display:
- SC126, Z180 Motherboard (eight x LEDs)
- SC129, digital I/O module (eight LEDs)
- SC134, LED outputs for RC2014 (eight LEDs)
The lack of specific support does not exclude the use of other hardware. It just means the ROM does not do anything specific with it.
Release notes
The Z180’s internal I/O is set to the range 0xC0 to 0xFF.
SCM assemble and disassemble commands only support official Z80 instructions, not the extended Z180 instruction set.
Small Computer Central 