Date   : Wed, 18 Apr 1990 03:54:00 GMT
From   : usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!geac!torsqnt!tmsoft!masnet!canremote!wayne.hortensiu@ucsd.edu (WAYNE HORTENSIU)
Subject: Z80 Users Manual bugs

>I then dug out "The gospel according to Carr" (The Z80 user's manual,
>by Joseph Carr, ISBN 0-8359-9516-X ) - It has the following table for
>what happens in a DAA.
 
I'd be *REAL* careful about relying on the Carr book for much of
anything - *ESPECIALLY* the DAA instruction. I got bit by one of the
many, many typos and just plain errors in this book once upon a time,
and it took me a long while to figure out that I wasn't doing anything
wrong - it was the book!
 
The exact problem? Carr lists the DAA instruction as being usable after
the following instructions: ADD, ADC, INC, NEG, SUB and SBC. Not true.
INC doesn't alter the Carry flag, and when that sucker's set, DAA does
Very Interesting Things (it adds too much to the most significant
nibble). I ran into this in an interrupt driven RTC - the time was being 
kept in BCD, and every time the interrupt happened when the Carry flag
was set, the time went gaga.
 
Other problems that I remember are missing opcodes in the opcode
listings, opcodes without detailed descriptions, etc. Carr is a very
nifty looking book - but it's not reliable information. 
 
wayne.hortensiu@canremote.uucp
---
 * Via ProDoor 3.1R 


End of INFO-CPM Digest V90 Issue #71
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