The latest release of this Firmware is detailed in the table below.
| Name | Small Computer Monitor |
| Configuration | F1 |
| Release date | 2022-10-16 |
| Download ROM image | SCM F1 2022-10-16 |
| Download source code | SCW 2022-10-16 |
| Device Programming: | |
| Code size | 32k bytes |
| Checksum (MiniPro 6.6) | 005B 35B8(AT27C256R) 01D9 B5B8 (SST39SF010A) |
| Recommended IC | AT27C256R-45PU, or SST39SF010A |
| Core Components: | |
| Monitor | Version 1.3.1 |
| BIOS | Z50Bus 1.3.1 |
| Included Apps: | |
| – ROM BASIC | Version 4.7b.1 |
| – CP/M loader from CF card | Version 1.0 |
The ROM image 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.
Source code is supplied (above) complete with the Small Computer Workshop development environment for Windows.
The Small Computer Monitor’s Components and Apps are described here.
Diagnostic and Status display
At reset, the system performs a self-test. The results are shown on the set of 8 diagnostic LEDs, if present, and the single status LED, if present.
Diagnostic LEDs: These should be off when the reset button is being pressed. Once released from reset, each LED should light in sequence for a fraction of a second and the test should end with all 8 LEDs being turned off. Failures are indicated as follows.
| Diagnostic LED display | Issue |
| LEDs always off | CPU not running, or Output port failed, or Reset failure |
| LEDs always on | Output port failed |
| Light sequence repeats indefinitely | RAM test failed |
| Light sequence then LED bit 0 remains on | Serial port test failed |
Status LED: This should be ON when the reset button is being pressed. Once released from reset, the LED should flash OFF for a fraction of a second and then stay on. Failures are indicated as follows.
| Status LED display | Issue |
| LED always on | CPU not running, or Output port failed, or Reset failure |
| LED always off | Faulty LED, or Output port failed |
| LED goes off and stays off | RAM test failed |
Supported Devices
- Z80 CPU (eg. Z84C00xx)
- SIO #1 at 0x80 (eg. Z84C4xxx)
- SIO #2 at 0x84 (eg. Z84C4xxx)
- CTC #1 at 0x88 (eg. Z84C30xx)
- CTC #2 at 0x8C (eg. Z84C30xx)
- ACIA #1 at 0xA2 (eg. 68B50)
- ACIA #2 at 0xA4 (eg. 68B50)
- Bit-bang serial port at 0x28
- CF Card at 0x90 for loading CP/M
- Diagnostic LEDs and digital I/O at 0xA0
- Status LED at 0x08
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 Cards
- Processor:
- Memory:
- Serial port:
- SC516, Z80 Processor card for Z50Bus
- SC527, Z80 Processor card for Z50Bus
- SC118, Z80 Processor card for Z50Bus
- SC511, Serial and timer card for Z50Bus (Z80 SIO & CTC)
- SC520, Serial ACIA 68B50 card for Z50Bus
- SC521, Serial Z80 SIO/2 card for Z50Bus
- SC125, Serial and timer card for Z50Bus (Z80 SIO & CTC)
- Timer:
- Baud rate generation:
- CP/M storage:
- Self-test status display:
- SC516, Z80 Processor card for Z50Bus
- SC527, Z80 Processor card for Z50Bus
- SC118, Z80 Processor card for Z50Bus
- SC506, Digital I/O card for Z50Bus (at 0xA0)
- Z50Bus, Digital I/O module (at 0xA0)
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
When using a bit-bang serial port, the Small Computer Monitor’s software timed idle events run very slowly. This is due to the time the processor spends handling the serial port. When a Z80 CTC is present, the timing of idle events is not dependent on software delays and therefore runs at the correct speed.
Older Releases
| Name | Small Computer Monitor |
| Configuration | F1 |
| Release date | 2022-02-27 |
| Download ROM image | SCM F1 2022-02-27 |
| Download source code | SCW 2022-03-01 |
| Device Programming: | |
| Code size | 32k bytes |
| Checksum (MiniPro 6.6) | 005B 5688 (AT27C256R) 01D9 B5B8 (SST39SF010A) |
| Recommended IC | AT27C256R-45PU, or SST39SF010A |
| Core Components: | |
| Monitor | Version 1.3.0 |
| BIOS | Z50Bus 1.3.0 |
| Included Apps: | |
| – ROM BASIC | Version 4.7b.1 |
| – CP/M loader from CF card | Version 1.0 |
Small Computer Central 