The latest release of this Firmware is detailed in the table below.
| Name | Small Computer Monitor |
| Configuration | S9 |
| Release | 2023-08-25 |
| Download | SCM S9 2023-08-25 (HEX) |
| Device Programming: | |
| Code size | 32k bytes |
| Checksum (MiniPro 6.85) | 07D2 268B (39SF040) |
| Recommended IC | SST39SF040 |
| Core Components: | |
| Monitor | SCM version 1.3.1 |
| BIOS | RC/Z180 version 1.3.1 |
| 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 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
This version of SCM supports the following devices.
| Device | I/O Address |
| Z180 CPU (eg. Z8S180xx), including: * Two asynchronous serial ports * Clock serial I/O for SD card * Timer | 0xC0 (to 0xFF) |
| Memory: (linear, no MMU) 512k Flash, 512k RAM | n/a |
| Status LED | 0x0E |
| Diagnostic LEDs | 0x00 |
| SIO serial #1 (SIO, but no CTC) | 0x80 (to 0x83) |
| SIO serial #2 (SIO, but no CTC) | 0x84 (to 0x87) |
| ACIA serial #1 | 0x80 (to 0x81) |
| ACIA serial #2 | 0x40 (to 0x41) |
| 8-bit IDE direct on CPU bus Compact Flash controller | 0x10 (to 0x17) |
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 modules
This version of RomWBW supports the following 80-pin RCBus modules (SC700 series).
| RCBus-80pin (700 series) | Function | I/O address |
| SC722 | Z180 processor, including: * SD card enable bit * Status LED * Internal registers | 0x0C 0x0E 0xC0 to 0xFF |
| SC721 | 1MB linear memory * 2 x 512kB Flash ROM * 1 x 512kB RAM | n/a |
| SC715 | Compact Flash interface | 0x10 (to 0x17) |
| SC719 | Digital I/O module (used for diagnostic LEDs) | 0x00 |
| SC716 | Z80 SIO/2 dual serial | 0x80 (to 0x83) |
| SC716 | Z80 SIO/2 dual serial | 0x84 (0x87) |
| SC705 | ACIA serial | 0x80 (to 0x81) |
| SC705 | ACIA serial | 0x40 (to 0x41) |
It also supports the following older modules (SC100 series)
| RCBus (100 series) | Function | I/O address |
| SC111 | Z180 processor, including: * Internal registers | 0xC0 to 0xFF |
| SC119 | 1MB linear memory * 2 x 512kB Flash ROM * 1 x 512kB RAM | n/a |
| SC145 | Compact Flash interface | 0x10 (to 0x17) |
| SC129 | Digital I/O module (used for diagnostic LEDs) | 0x00 |
| SC104 | Z80 SIO/2 dual serial | 0x80 (to 0x83) |
| SC104 | Z80 SIO/2 dual serial | 0x84 (to 0x87) |
| SC132 | Z80 SIO/0 dual serial | 0x80 (to 0x83) |
| SC132 | Z80 SIO/0 dual serial | 0x84 (to0x87) |
| SC139 | ACIA serial | 0x80 (to 0x81) |
| SC139 | ACIA serial | 0x40 (to 0x41) |
The SIO can either use the RC2014 addressing scheme or the typical Zilog scheme (as used by Dr. S. Baker’s SIO module)
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.
Incompatible modules
Modules not compatible with this configuration:
| Device | Comment |
| SC706 SC708 SC108 SC153 | Only one CPU supported and it needs to be a Z180 |
| SC725 | Z80 SIO serial + CTC sort of works but problematic with Z180 |
| SC707 SC714 SC143 SC150 SC151 SC152 | Only 1MB linear memory supported |
| SC110 | Serial module requires bus clock 7.3728MHz |
The official RC2014 SIO module does not have tight address decoding so it appears as an SIO at both 0x80 and 0x84.
The addresses of the official RC2014 SIO and ACIA modules clash, so they can’t both be installed at the same time. Third-party modules often have address options to avoid this problem.
Release Notes
The Z180’s internal I/O is set to the range 0xC0 to 0xFF.
Small Computer Central 