Software Counter/Oscillascope

[Colin Fraser]

----- Original Message -----
From: "Plutonique9" <Plutonique9 at symbiocom.com>
To: <synth-diy at node12b53.a2000.nl>
Sent: Tuesday, January 09, 2001 5:46 AM
Subject: Software Counter/Oscillascope


> The last thing that i feel sus about in this unit is maybe the CPU
> clock and/or "INT Clock" (is this interupt clock?) is mis aligned.
> The "Int clock" adjustment is made via trimmer TM1 while the CPU is
> one of those tuning coil "thingie majigs".
> I asked this question on AH with no responce about what the symtoms
> of an mis alligned CPU clock and INT clock would be in an XOX
> machine???

Can't say for definite, but my guess is that the interrupt routine on the
606 (and 303) is responsible for scanning the keys and lighting the leds.

The din clock input does not trigger the interrupt line - it goes to a
normal port input, which leads me to believe that the clock input is
therefore polled by the main program loop.

This is borne out by the fact that the interrupt period is supposed to be
1.8 ms.
A 606 needs a sync pulse of at least over 1 ms in order to keep good time.
If the polling of the clock input is interrupted by a routine that lasts say
half of the 1.8ms period, that would tie in with the required clock pulse
length. If the clock pulse were too short, it would be missed during the
interrupt routine.

Unfortunately if this is correct, then it would make no difference at all to
pattern writing.

One of these days, I'm going to hook a scope up to the key scan and led
lines, and see if the scanning frequency is directly related to the
interrupt clock frequency. If so, then the above theory is correct.

Colin f