26 Jan
2010
26 Jan
'10
10:59 a.m.
Dan Gahlinger wrote:
I keep thinking it was the 6520 or 6522 processor in
the 1541
which had the cool dual-clock ability.
1/2 a clock running as one mode, the other 1/2 as another mode,
technically running two instructions at once. so to speak.
Not sure about the 6520, but the 6522 certainly did - that was the VIA,
had two timers and different modes for both, but T2 was less powerful
from what I recall.
I think the C64 had an update
to this chip called the CIA 6526 instead
off the VIA. (Complex instead of Versatile?). Pet's and the Vic 20's
had 6522's.
The clocks could also be used to count pulses, or be used to
reload/repeat - that's how you got sound on the Pet's - you'd program
one of the timers to loop, and it was attached to a piezo.
The rate you set the timer to was the frequency of the sound.