www.mycpu.eu (C) 2017 by Dennis Kuschel 


This page lists all known problems and possible fixes.


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 www.mycpu.eu (C) 2017 by Dennis Kuschel 


Regards:
RAM Extension Boards with Version Number v2 (Memory Self-Build-Guide 070623 or earlier)

Abstract:
There is a bad error on the Memory Extension Board. The Bug leads to a system crash when the Operating System tries to execute a program from the high memory area above 512KB. The CPU can load a program into that high RAM area - but it can not execute the code. This is caused by an erroneous signal decoding of the signals that are used to steer the access to the both 512KB RAM's. When the CPU enables the /RDROM signal to fetch the next OP-Code from the RAM, some address lines of the both RAM's IC16 and IC29 are not driven correctly (they are floating and pulled-up to +5V).

Bug-Fix:
Download the PDF that describes how to fix the bug.

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 www.mycpu.eu (C) 2017 by Dennis Kuschel 


Regards:
VGA Graphic Unit (Graphic Unit Self-Build-Guide 070704 or earlier)

Abstract:
The resistors R27, R28 and R29 have a too high value (120 Ohm) in the original design. This leads to the effect that most of the modern TFT Displays display only 8 of the possible 16 colors.

Bug-Fix:
To fix this problem the value of the three resistors must be reduced to 47 Ohm. You find the resistors on the bottom-right side of the Interface Board, near to the D-Sub connector.

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 www.mycpu.eu (C) 2017 by Dennis Kuschel 


Regards:
One or both of the RS232 interfaces on the Multi-I/O-Board does not work properly.

Abstract:
Depending on the populated UARTs it may happen that you get garbage printed to the terminal screen, or you will fail to connect to the remotefs-server on com2.

Bug-Fix:
Replace all 74ACxxx -parts on the board by their 74HCxxx equivalents. With this change it may be necessary to decrease bus speed by inserting waitstates. Please see chapter 1.5.4 in the MyCPU self build guide for details.

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 www.mycpu.eu (C) 2017 by Dennis Kuschel 


Regards:
Wait State Logic on MyCPU v2.2 Interface board

Abstract:
In most cases the wait state logic on the MyCPU Interface Board does not work properly. In some rare cases the logic works, but that depends on the speed and type of the used integrated circuit parts.

Bug-Fix:
First check if your board has the bug. Please check if pin 2 of IC63 is connected to VCC (this is pin 14 of IC63). If so, your board has the bug.

To fix the bug, cut the wire at the bottom side of the PCB that goes from pin 2 to pin 14 of IC63. Then take a piece of wire make a new connection between pin 2 of IC63 and pin 11 of IC30. Thats all. (IC63 is a 74AC00 and IC30 is a 74HC393)

This bug is fixed on MyCPU23

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 www.mycpu.eu (C) 2017 by Dennis Kuschel 


Regards:
Display Errors with VGA Unit

Abstract:
With some mixture of components the VGA Unit won't display an error free picture.
Some RAM memories seem to be unsuited for use with the VGA Unit.

Bug-Fix:
Use only fast memories. This regards the two 62256 RAMs in the VGA Unit.
Use components that are rated at 70ns or faster. Some 70ns types may fail.

Sometimes it may also help to replace IC25 and IC26 on the Counter Board by faster 74AC541 chips.


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