Parity Checking in CPUs (was: Byte sizes...
zmerch at 30below.com
Tue Mar 15 13:32:18 CST 2005
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.
> Even if the parity checking is a lowly 74180, like
>in a microcomputer - it is still not boggin down the processor. The
>processor really doesn't need to know about parity, unless things go bad.
Altho it's not a *huge* need, it can be handy for serial I/O... that would
be a function that uses parity, but is not reliant on the memory controller.
Roger "Merch" Merchberger
Roger "Merch" Merchberger | "Bugs of a feather flock together."
sysadmin, Iceberg Computers | Russell Nelson
zmerch at 30below.com |
More information about the cctalk