DS12887 pcb substitute with battery

[Tony Duell]

On Sun, Jan 22, 2017 at 5:16 PM, Jon Elson <elson at pico-systems.com> wrote:
> On 01/22/2017 10:07 AM, Ali wrote:
>>
>> Al,
>> I thought the problem with switching these chips was that part of the ROM
>> code was embedded in them? I.e. it isn't just an issue of battery? Am I
>> wrong? If I am then why not use one of the replacement chips that are
>> available?
>>
> These don't have a lot of memory on them.  many early PCs stored some config
> info there, but generally the BIOS can reconstruct it if it isn't there.  I
> suppose there is a possibility that random data in the CMOS memory could
> cause the BIOS to try to use unavailable features and hang.  I don't think
> anybody put actual executable code in there.

On most PCs the RTC chip is mapped as I/O ports, not memory, so you couldn't
execute code from its RAM anyway. I suppose on (say) a 68000 based machine
you could (there is no separate I/O port address space on that processor) but
I have never seen it done.

-tony