Re: HP41 Card Reader 1E Message #2 Posted by Eric Smith on 17 Aug 2011, 12:49 p.m., in response to message #1 by Richard L. Taylor
That's a well-known bug in early versions of the card reader ROM. It happens with any function that gives a three-digit prompt, and I think it may happen under some circumstances for two-digit prompts.
I'm not sure whether it is fixed in 1F, but I believe it is fixed in 1G. A more serious bug fixed in 1G is that the card reader can corrupt the contents of an extended memory module in port 2 or port 4.
I spend some time studying the backarrow bug last month, and found that it was due to the card reader ROM overflowing the four-level hardware return stack in the I/O service poll.
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