🚀 go-pugleaf

In article <342.filbo@deeptht.santa-cruz.ca.us> belal@sco.COM (Bela Lubkin) writes:
>Can anyone email me, or point me to a datasheet for the Motorola
>MC146818 Real Time Clock chip used in IBM AT type computers?
>
>What I'm most looking for is a table of the possible values for bits 3:0
>of "status register A" -- the "rate selection bits".  The documentation
>I have says that the IBM BIOS initializes these bits to 0110, thus
>selecting a 1024 Hz square wave.  Unfortunately, it doesn't bother to
>document what the other 15 combinations mean.  If you have only a
>printed datasheet, let me know if you're willing to type in that table.
>
>I suspect there's a lookup table in the chip, and that there might be
>different versions of the chip with different lookup tables.  Any
>further information or warnings about that would be appreciated.
>
>If I receive an online datasheet I will make it available to others;
>send me a request now (via email).  I do not intend to post it -- the
>concept of a "summary" of a datasheet doesn't seem to make much sense...
>
>Thanks in advance!
>
>Bela Lubkin  * *  //  filbo@deeptht.santa-cruz.ca.us    ZURC ATNAS morf EVIL!
>     @     * *   //  belal@sco.com   uunet!sco!belal  uunet!sco!deeptht!filbo
>R Pentomino  * \X/  Filbo @ Pyrzqxgl +1 408-476-4633 and XBBS +1 408-476-4945

Not quite a data sheet but here's the table:

                 4.194304 or 1.048576 MHz
                      time base
                Periodic Int   SQW Output
RS3 RS2 RS1 RS0    Rate           Freq
 0   0   0   0    None            None
 0   0   0   1  30.512 us      32.768 kHz
 0   0   1   0  61.035 us      16.384 kHz
 0   0   1   1  122.070 us     8.192 kHz
 0   1   0   0  244.141 us     4.096 kHz
 0   1   0   1  488.281 us     2.048 kHz
 0   1   1   0  976.562 us     1.024 kHz
 0   1   1   1  1.953125 ms    512 Hz
 1   0   0   0  3.90625 ms     256 Hz
 1   0   0   1  7.8125 ms      128 Hz
 1   0   1   0  15.625 ms      64 Hz
 1   0   1   1  31.25 ms       32 Hz
 1   1   0   0  62.5 ms        16 Hz
 1   1   0   1  125 ms         8 Hz
 1   1   1   0  250 ms         4 Hz
 1   1   1   1  500 ms         2 Hz