24 Sep
2008
24 Sep
'08
10:45 a.m.
I don't remeber who made the chip, but I made several diy z80 machines
using a 279x. The 279x had an internal pll data seperator. All that was
needed externaly was a cap and resistor as I recall.
I remember 3 external adjustments (1 trimmer capacitor, 2 pots) and a few
fixed R/s and C/s, but nothing much more. Setting up is easy if you have
a 'scope, you put the chip into a test mode (by grounding one of the
pins) and then you get 3 signals on 3 of the pins each one of which is
affected by one of the adjustments. So that, for example, you adjust the
rimmer capacitor to get the right VCO free-running frequency, the VCO
output is available on one of the pins in test mode.
This chip was commonly used in HP HPIB and HPIL disk drive units, which
is where I've had to set it up.
-tony