[fpc-pascal] timing again

["Vinzent Höfler"]

> The standard clock for the system timer runs at 1,193,182 Hz, derived 
> for the original IBM PC as the 4.77 MHz processor clock divided by 4.

Digging a bit deeper clarifies it:

http://sos.enix.org/lxr/source/hwcore/i8254.c?v=6.5

|* Ahhh PC systems are nice toys: this maximum "strange" frequency
|* equals that of the NTSC clock (14.31818 MHz) divided by 12. In
|* turn, the famous 4.77 MHz cpu clock frequency of the first IBM PC
|* is this same NTSC frequency divided by 3. Why the NTSC frequency as
|* a base "standard" ? Because the 14.31818 MHz quartz were cheap at
|* that time, and because it allows to simply drive altogether the
|* cpu, the "time of day" timer, and the video signal generators.

So, the base frequency actually was a 14.318 Mhz quartz, not a 13.125 as I assumed in my previous post.

But that's enough history lessons for a day. ;)


Vinzent.

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