SC518 is a Z80 CPU card designed for Z50Bus.

Card features:

• Z80 Central Processor Unit (CPU)
• Jumper to select one of 5 clock sources
• Typical clock speed 7.3728 MHz
• Compatible with memory card SC519

This card is designed to allow easy selection of a number of different clock sources for the Z80 CPU.

Clock source

The clock source is selected by fitting a jumper shunt to the required position on JP1. The available clock sources are:

• External pin (pin 5 of connector P2)
• Oscillator X1 (half-size 8-pin DIP ‘can’ oscillator)
• Oscillator X2 (half-size 8-pin DIP ‘can’ oscillator)
• Oscillator X3 (half-size 8-pin DIP ‘can’ oscillator)
• Bus pin USR1 (pin 39 of the Z50Bus)

Up to three oscillators can be fitted (X1 to X3). This allows three different clock speeds to be readily available.

Alternatively, the clock signal can be provided on the Z50Bus pin 39 (USR1) or an external signal pin on connector P2. These signals can be clock rates from D.C. (zero Hertz) to the maximum the Z50Bus can support (typically 8 MHz but with suitable components, it could be 20 MHz).

System requirements

In order to build a minimal working system you will also need:

• Backplane, eg:
  • SC501 – 7-slot backplane
  • SC508 – 10-slot backplane
  • SC513 – 6-slot backplane plus 5-volt power input
  • SC515 – 14-slot backplane
  • SC522 – 6-slot backplane
• Power supply, eg:
  • SC502 – Power supply card (8 to 15 volt input)
  • SC513 – 6-slot backplane plus 5-volt power input
• Memory card, eg:
  • SC519 – 128k Flash ‘ROM’ plus 128k RAM
• Serial card, eg:
  • SC511 – Z80 SIO (2 ports) plus CTC (baud rates and timer)
  • SC520 – ACIA 68B50 (1 port) plus baud rate generator
  • SC521 – Z80 SIO (2 port) plus baud rate generators