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

[river]

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