The latest release of this Firmware is detailed in the table below.

Name	Small Computer Monitor
Configuration	S3
Release	2022-02-27
Download	SCM S3 2022-02-27 (HEX)
Device Programming:
Code size	32k bytes
Checksum (MiniPro 6.6)	005B 1AD2 (AT27C256R) 01D9 9AD2 (SST39SF010A)
Recommended IC	AT27C256R-45PU (32kB) SST39SF010A (128kB)
Core Components:
Monitor	Version 1.3.0
BIOS	SCZ80 1.3.0
Included Apps:
– ROM BASIC	Version 4.7.1
– 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

• Z80 CPU (eg. Z84C00xx)
• 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 0x00

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. Third-party modules often have address options to avoid this problem.

The official RC2014 SIO module does not have tight address decoding so it appears as an SIO at both 0x80 and 0x84.

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

• Processor:
  • RC2014, Z80 CPU module, plus:
    • RC2014, dual clock module
  • RC2014, Z80 CPU (Classic/2 kit), plus:
    • RC2014, clock module (Classic/2 kit)
  • SC108, Z80 CPU, RAM, ROM and clock module

• Memory:
  • RC2014, memory module pair:
    • RC2014, 64k RAM module, plus
    • Pageable ROM module
  • SC108, Z80 CPU, RAM, ROM and clock module
  • SC143, ROM module, plus
    • RC2014, 32k RAM module (Classic/2 kit)

• Serial port:
  • RC2014, serial module (68B50 ACIA) – retired
  • RC2014, serial module, 68B50 ACIA (Classic 2 kit)
  • RC2014, dual serial module (Z80 SIO/2)
  • Karl’s #61, serial and storage (ACIA & CF)
  • SC104, serial module (Z80 SIO/2)
  • SC110, serial and timer module (Z80 SIO & CTC)
  • SC114, bit-bang serial port (9600 baud)
  • SC132, serial module (Z80 SIO/0)
  • SC139, serial module (68B50 ACIA)
  • and others

• Timer:
  • SC102, counter timer module (Z80 CTC)
  • SC110, serial and timer module (Z80 SIO & CTC)

• Baud rate generation:
  • RC2014, dual clock module
  • SC102, counter timer module (Z80 CTC)
  • SC110, serial and timer module (Z80 SIO & CTC)

• CP/M storage:
  • RC2014, compact flash module
  • Karl’s #10, compact flash module
  • Karl’s #61, serial and storage (ACIA & CF)
  • Karl’s #72, compact flash module
  • Karl’s #73, compact flash module
  • SC145, compact flash interface module
  • others

• Self-test status display:
  • RC2014, digital I/O module (eight LEDs)
  • SC114, Z80 motherboard / SBC (single status LED)
  • 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.