🚀 go-pugleaf

In article <JT.92Oct13155753@fizyk1.fuw.edu.pl> jt@fuw.edu.pl (Jerzy Tarasiuk) writes:
>If the timer gots bad frequency, what way can measure time ? DOS takes
>time from the chip and even small change of the frequency would result
>in bad values from DOS 'TIME' command. On AT can use CMOS clock to
>verify 8253 timer has good frequency, but on XT there is no way unless
>know all possible clock/calendar cards and use time get from such a card.

This is the problem we had with one particular clone in that the DOS
time was always off due to the wrong clock frequency on the 8253 clock
chip.  The designers did not want to change the crystal.  They felt
that the home computer users (which is what this model was targeted
for) could live with the error.

>Another reason for the 8253 should always get correct clock is its clock
>is derived from CLK signal on bus which is used by CGA to form signal for
>TV set which color decoding can be very sensitive to frequency errors.

I have no clue to the relationship between the 8253 clock, the bus CLK
signal and the color burst clock.  I only know that the 8253 clock
signal generally has its own crystal and in at least one case I have
seen, its crystal frequency was not correct.

>Note I stated don't need to know CPU clock.

I think I missed something then.  What clock frequency are you trying
to determine?

-- 

rap.

-----------------------------------------------------------------------
Robert A. Pease, Novell Inc.
Internet: rap@novell.COM
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rap.

-----------------------------------------------------------------------
Robert A. Pease, Novell Inc.
Internet: rap@novell.COM