Z80 home brew with FDC

Tony Duell ard at p850ug1.demon.co.uk
Wed Sep 24 12:45:50 CDT 2008

> 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.


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