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| From: Marko_Mäkelä
Date: 2000-07-25
Subject: Re: ADC - SBC
|
On Tue, 25 Jul 2000, Almos Rajnai wrote:
> 1. What exactly happens when I am trying to add a number to a non-
> decimal coded number (semi-tetrade?) in decimal mode.
I investigated this in 1993 or so. The results are documented in a file
"64doc" that you can find e.g. on ftp.funet.fi. The document includes a machine language program that emulates these instructions in decimal mode
(e.g. it checks whether an emulator implements the decimal mode properly by testing all 2*256*256 combinations).
> 2. In decimal mode ADC and SBC how implements carrying (carry flag)?
See above. The program also emulates the Carry, Negative and oVerflow flags.
> 3. When will be overflow flag set at ADC and SBC commands? (In non-
> decimal and decimal mode too.)
See above. In binary mode, it's pretty straightforward (but I don't remember it right now).
Marko
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