🚀 go-pugleaf

Yes, it is possible to read the CMOS clock and RAM quite easily, but do you
mean a PC or an AT? (the original, 8088, PC CMOS is totally different).

For an 8088 PC, to read the CMOS (assuming it has it), you need to know the
starting port address, which varies from board to board.  The best idea is to
try some likely ports, avoiding known system ports of course, and see if one
has a valid hex number seems to be cycling 1000 times a second (or something 
like that).

For an AT, there is always ports 70h and 71h, and you use them like this...

output a number (0 to 3Fh) to port 70h, saying which CMOS clock/RAM cell you
want, then

read or write port 71h (1 byte of data).  Be careful not to access port 70h
without also accessing port 71h - apparently it can ruin the chip. Also be
aware that you can get "false" readings (255) from the clock registers at
times.

The PC/XT CMOS RAM has a separate port addresses for each cell (but has less
cells, and the clock cells are in a different order.

For more information, have a look at the documenation file that comes with my
program CMOS299.ZIP, or at the INFOPLUS package, that has sources.  (Actually,
you can get the sources to my CMOS setup program too if you ask nicely).

Hope this helps,
Mark Aitchison, University of Canterbury.