[sdiy] New to list - and DSP development

[Rainer Buchty]

>No, you had 14,31818 MHz = 4 * 3,579545 MHz. You also had the CPU running at
>14,31818 MHz / 3 = 4,7727267 MHz (if you guys where wondering wherever that
>came from).

Should have checked the ISA specs first...

>1,8432 MHz = 96 x 19,2 kHz
>
>The ratio between these are now 14,31818 MHz / 1,8432 MHz which is about
>7,7681. This is why the serial interfaces had their own crystal oscillator at
>1,8432 MHz.

Now I wonder how those cards which get their timing from the ISA bus
"high-speed" clock (i.e. 14.31818) manage to get a 7.7681 divisor. I
have to cards which don't employ any (visible) 1.8432MHz oszillator but
instead take the high-speed clock into one of those "I do LPT plus 2
COM ports and don't ask for any datasheet" chips.

>When IBM created the IBM PC they did these choices. I guess they had the
>intention that graphical cards would easilly be able to be simplified by
>already operate synchronous with the NTSC colour-burst.

Ah, maybe they just stole the idea from Clive Sinclair who based his
early machines' timing entirely on video timing :)

>> As you say, MIDI timing is based on an even multiple of 1MHz. If you
>> want to convert any vanilla serial card to MIDI, either apply
>> 16MHz to the 14.7456MHz input or 2MHz to the 1.8432MHz input. Then use
>> OS settings for 28k8 to get 31k25.
>
>Except for the numbers not being quite correct, yes.
>
>You could do that by replacing the 1,8432 MHz crystal with a 2 MHz
>crystal and the choose 28,8 kBd.

Uhm, yes. That was what I was writing: "...apply 2MHz to the 1.8432MHz
input. Then use OS settings for 28k8 to get 31k25".

>Standards are good, everyone should have their own, but in reality everyone
>run multiple standards for themselfs.

There's nothing wrong with multiple standards. Leaves room for an
interface market :)

Rainer