www.mycpu.eu

(C) 2023 by Dennis Kuschel

In some configurations, dependend on used parts or the length of the backplane bus, the MyCPU seems to be very instable and crashes often. This page collects all known fixes that may increase your system's stability.


If you observe stability problems of your MyCPU please check this list:

• MyCPU Interface Board V2.2
  • Fix the bug in the waitstate logic
  • Enable waitstates (set Jumper JP5 to position 1-2)
  • Add an extra wire on the CPU interface board to strengthen GND connection
  • Add 10nF SMD capacitors parallel to 100nF capacitors
  • Replace IC31 by a 74HC74
  • Reduce oscillator frequency, use oscillators in the range of 16 to 20 MHz
  • Last chance here: Replace IC22 and IC29 by their 74HCxxx counterparts

• MyCPU Microcode Control Board
  • Try different positions for Jumper JP4
  • Use 74HCxxx types for ICs 6, 7, 12, 13, 14 and 15
  • Use faster EPROMs

• MyCPU Signal Decoder Board
  • Use a 74HC138 for IC20, -or-
  • insert 47 Ohm resistors in the signals at IC20 pin 11 and pin 12 (use SMD type resistors on board top layer)

• Backplane Bus
  • Place the CPU at the very left or very right end on the backplane
  • Place the Power Supply at the other end (it includes termination resistors)
  • Try different positions for the other boards on the bus

A common method to reduce stability issues is:  Don't use 74ACxxx -parts at all!
The second method is to reduce oscillator frequency to 16MHz or lower.


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