Card reader bug

There is a card reader bug that is present in the 1E version of the card reader (and probably 1D), and fixed in the 1G version. I haven't got a 1D or 1F to check. I discovered the bug around 1981, and I think I saw it mentioned by someone else in the PPC Journal at one point.

With the card reader plugged in, press the key sequence

GTO . EEX 0 0 backspace backspace
What you should see after that is
GTO .1__
If you have the bug, the display rotates so it reads
0      GTO .1

From study of a instruction trace, it appears that the bug is due to the card reader ROM's I/O service poll routine violating one of the requirements of the mainframe polling code. From the mainframe source code:

All subroutine levels are available except in I/O service entry.
If PKSEQ is set then I/O service routines must either preserve
three subroutine returns on the subroutine stack or else terminate
the partial key sequence.

The CR-1E I/O service poll code uses two levels of subroutines. Perhaps the CR-1G ROM was changed to not need two levels of subroutines, though I haven't yet disassembled the code to determine what the actual changes are.

Hi, Eric,

Mine has the bug, but how can I tell which version it is?

The serial number is 2036S45246, if that's any indication.


--- Les



I have about 5 of these, let me check. Four on the table being restored as we speak.

Version is seen by catalog function.



Mine just says "CARD READER", Geoff - no version number at all.


--- Les



I have a 1E, 1F, 1G and three that state Card Reader only:

display version serial number

CARD RDR 1E 2056S46900
CARD RDR 1F 2319S81056
CARD RDR 1G 2703S80162
CARD READER ?? 2044S45132
CARD READER ?? 2023A00100
CARD READER ?? 1935A00179

It would seem that the early card readers just state "CARD READER" with a CAT II display.

I will check the bug on 1F and I think Wlodeks book mentions it in the bug section.

Cheers, Geoff


Without a version letter in the catalog, it is probably 1D. I haven't heard of anyone finding the earlier versions, so 1A-1C were probably only in prototypes.

If you really want to check, you can use the diagnostic ROM's ROM check, which will display the full identifier, or you can use the ZenROM or other means to look at ROM locations EFFB through EFFE.


other means to look at ROM locations EFFB through EFFE

Function PGTRAIL in the TOOLBOX-II module (and others) will show the last four words before the checksum (a.k.a. the "page trail"). Input is the page#, 0-15.


I don't have those ROM's, but comparing with Geoff's serial number list, I'd say it's a 1D.


--- Les


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