8 Feb
2015
8 Feb
'15
5:21 p.m.
On Sat, 7 Feb 2015, Brent Hilpert wrote:
On 2015-Feb-07, at 8:47 AM, Noel Chiappa wrote:
You shouldn't need to do anything regarding pin 1, (this) datasheet
indicates they (the FOX F5C-2 series) have an internal pull-up R on pin
1, so the output should be active by default.
http://www.datasheets360.com/pdf/8636385546948709069
I checked 4 of the F5C-2 parts at random, and measured ~95k-96k between
pin 1 and pin 14 (vcc) and infinite resistance (or at least off the scale
on my Fluke DMM) between pin 1 and pin 7 (gnd). I guess that means they do
indeed have some sort of internal pull-up resistor, but it certainly isn't
much of one. OTOH, that makes sense since a larger value pull-up would
limit current draw if you ground pin 1 to disable the oscillator.
From:
Tothwolf
Before I forget again, did you check for +5V on
pin 1 (enable) when
you were testing your existing oscillator?
Wow. Never thought to try that. Then again, I don't look for +5V on
your average 74xxx when I'm debugging, either! :-) I mean, it's a
trace, the solder on the pin looks good, that's as far as I go,
usually! And there's nothing shown as connected to that pin on the
circuit diagram.
So I looked, and... it's at ground (or floating). The only pin that has
anything is 14, at +5V (expected). But I looked online for some
datasheets for similar oscillators, and some of them say 'pin 1 - N/C'.
Are yours tri-state? (That's the enable pin on the tri-state ones.)
I suppose even if yours are tri-state, I can still use them; a quick
ohmmeter check shows that pin 1 isn't connected to either power or
ground, so I can probably tie it high (via a resistor, which in
addition to being normal practise, will prevent a major disaster in
case I'm confused - a state I'm often in :-). As your fault description sounds like it could be
stuck in tri-state,
you could try an experiment with your existing osc. and pull pin 1 high
through an R to see if it activates, on the small probability the
internal fault is loss of that internal R.
This does make me wonder even more what may have gone wrong in Noel's
oscillator. I am familiar with some of these type of oscillators (and
crystals) growing tin whiskers inside their cans, and I'm really starting
to wonder if that's what caused that oscillator to fail.
I have one 13.824 unit I was going to offer but
Tothwolf has lots of
them, so all the better there. They are a baud-rate generator frequency
for the standard (300..9600..19200...) baud rate series as well as the
14400..57600.. series. Could probably be found in some 90s-era modems.
That makes sense. I'm almost 100% certain these parts did indeed come from
an auction of a company that designed ASIC parts for modems (POTS, leased
line, and ISDN) that closed one of their R&D labs in the 90s. I know for
sure I still have some prototype 9600 and maybe even some 14400 modems
that came along with the parts cabinets I bought.