23 Sep
2008
23 Sep
'08
1:13 p.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.
Les
23 Sep
23 Sep
3:01 p.m.
On Sep 23, 2008, at 1:13 PM, les at frii.com wrote:
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.
Western Digital. These are really nice chips, but they're pretty
expensive nowadays.
-Dave
--
Dave McGuire
Port Charlotte, FL
24 Sep
24 Sep
1:45 p.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
4:06 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.
25 Sep
25 Sep
2:08 p.m.
Tony Duell wrote:
Yep that's pretty much the same procedure that I have used with this chip.
Not suprising, I got it from the WD databook. HP don't regard these
adjustments as being able ot be preformed in the field, but considering
they provide a test jumper on most of the PCBs and labelled testpoints, I
don't see what the problem is. (This is the same HP, I guess, that state
that SMD parts are not field-replaceable...) But anyway..
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.
The HP units I mentioned use the 600 rpm Sony 3.5" drives, so the data
rate for a normal double-desnisty disk ('720K' to PC types) is 500kbps.
-tony
5760
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4 comments
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afra＠aurigae.demon.co.uk -
ard＠p850ug1.demon.co.uk -
les＠frii.com -
mcguire＠neurotica.com