24 Sep
2008
24 Sep
'08
1:06 p.m.
Tony Duell wrote:
Yep that's pretty much the same procedure that I have used with this chip.
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.
The Dragon 32/64's DOS cartrige also used the 2797, as did the two
prototype machines Dragon Data made just before they went to the wall in
1984 :(
The chips can also deal with the 500K/s data rate that 8" and 1.44M
drives use.
IIRC the WD1770/72 which though less flexable than the 279x series also
has an internal data seperator, though can only do single and double
density.
Cheers.
Phill.
--
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
"You can twist perceptions, but reality won't budge" -- Rush.