New subject: Parity Checking in CPUs

16 Mar 2005

Hi,

...
 Rumor has it that William Donzelli may have mentioned
these words: 
...
 >Parity checking is the job of the memory
controller, not the processor. In
>fact, I am having a hard time thinking of a processor that did its own
>parity checking in software (yes, I know any processor could do it, but
>did any really do it?). 
...
 8085? There's a P bit in the condition code
register (in 6809 speak) -- I 
think it's called the PSW -- Program Status Word? I'm just beginning 
learning assembly on my Tandy 10x/200 machines... Anyway, there are several 
arithmetic operations that automatically set the Parity bit and there are 
branch and return instructions that utilize the status of the P bit. 
Yes, the 8080/8085/8086 series chips did parity checking. The PSW had a flag
for odd/even parity. Naturally, the Z80, being a superset of the 8080, also had this
ability. I assume that the later generations of x86 series chips, for backward
compatability,
also had the ability to check for parity.

The TMS9900 series also did parity checking.

...
 From a cursory glance at the status registers of the
6809 and 68000 processors, it appears these devices did not have inherent parity
checking.

river

Parity Checking in CPUs (was: Byte sizes...