Clock and Reset Module


This module provides the clock signal for the CPU and the ACIA.  Nominally it runs at 7.3728Mhz which most Z80 CPUs are happy with (even 4Mhz ones) and equates to 115,200bps communication from the 68B50 Serial I/O module.  Using a 3.6864Mhz crystal will half the CPU speed and drop the serial down to 57,600bps.

The reset circuit pulls the !reset pin high, and a momentary tactile switch sets it low to reset the CPU.  Note that the reset circuit is duplicated on the Backplane-8 and either or both can be used.


Note that the Gnd, Vcc, Reset & Clock pins are marked on the PCB and these must be carefully lined up with the appropriate sockets on the backplane.


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Bill of materials

  • 8 pin RA Header
  • 14 pin narrow DIL socket
  • 74HCT04
  • 7.3728 Mhz Xtal
  • 22pf ceramic cap
  • 1M resitor
  • 1k resistor
  • 2k2 resistor
  • SPST Push Switch
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