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The CMOS page on the wiki links to two CMOS memory maps.

The first one says the bit 0 of register B deals with DST, bit 1 is 12/24 hour mode, and bit 2 is BCD or BIN. The second one, however, says bit 1 is DST, bit 2 is 12/24 hour, and doesn't give a BCD/BIN bit.

The wiki seems to follow the first one, but Bochs follows the second, so I assume the second is the more correct version. If that's so, is there not a BCD/BIN bit or is it somewhere else?

Hi,

Looking at this part of the Bochs source code, it looks like Bochs follows the first one.

For my reference material, I looked at an old document called "PCTIM003.TXT" (which is awesome and covers all timing on old 80x86 machines) and it follows the first one too. The I looked at Ralph Brown's Interrupt List (which comes with a CMOS list, an IO port list, etc) and it also follows the first one (with no mention of the second).

Mostly, as far as I can tell; everything uses the first version, and it's very likely that the second one is wrong.


Cheers,

Brendan