The 8170 isn't smart enough to calculate the leapsecond immediately.
Instead, it uses its error correction routine which takes about 4
minutes after the event to realize that it is one second off, then
updates the time to match. Details quite far down the page at
http://www.febo.com/pages/leapsecond_2005/
John
----
On 2/22/2012 2:48 PM, Jim Hickstein wrote:
On 2012/01/23 15:28, Jim Hickstein wrote:
Reviewing the schematic for the 8170 (I'll get back to the setting
coil in the
clock a bit later), my unit does not seem to have Option 18 and A4-U4,
the 8255A
at its heart, is not populated. A pity: it would have lovely BCD
outputs and an
on-time pulse, just what I need. (The recent discussion of multiplexed
7-segment
LED outputs tells me I don't want to try to detect ":00:00" or
":59:59" there.)
What are the chances my EEPROMs would DTRT if I just added an 8255A to
this
board?
Looking better today. I dragged a scope up from the basement. CS is
getting hit, about 11 times, near the beginning of each second (image).
I guess this means I have to design the circuit, now, and place an order
for some parts.
> What other components should I add to complete the Option 18
installation?
A3U4, the 8255A, seems to be the only thing missing, apart from A3J4,
the 50-pin header that connects to a cable to bring these BCD signals
out to the rear panel DD-50, also missing. For my purposes I can stop at
the header. It'll be a nice place to mount a little daughterboard. This
is on sheet 4 of A3, the uP board schematic, not on a separate sheet as
some other options are.
If I need different EEPROMs to enable Option 18, where could I get the
image?
(The parts and the programmer I can probably get.)
Perhaps I'll do a socket and the 8255A first, just to see the output
pins move as expected. This means paying Digikey for shipping twice. Oh,
well. (Anyone near http://www.airnav.com/airport/KMSP got an 8255A lying
around? I have some Augat 40-pin sockets left over from 1983, packrat
that I am.)
Maybe I can get it done in time to have it send a pulse to the clock
during :59:59 _or_ :59:60. :-) I don't recall if an 8170 is quite that
savvy, to produce this on its output, but the BCD encoding could do it.
We'll find out, eh? And the clock will be set properly the next hour,
anyway.
On 2012/01/20 16:23, Jim Hickstein wrote:
I have a Spectracom 8170 in the living room (who doesn't?), and a
Western Union
time-service clock, a.k.a SWCC clock -- a nice one, in a 3-foot-high
wood case.
I've been watching TV with this combination for years and years but
never got
around to feeding a pulse from the 8170 to discipline the other one.
Now that
Western Union no longer provides the service. :-) But it just begs to
be done.
I did draw up a TTL circuit, once (on a napkin, naturally, which I
have now
misplaced), that could live inside the 8170. I figured out the
minimum number of
inputs needed to detect when the MM:SS LED displays said 00:00 (for
one second).
It would close a relay, which could feed the winding-battery power to
the
hour-set solenoid down a pair of wires from 10 feet away. But I never
built it.
A little over a year ago the TS clock was getting gummy and
free-running slower
and slower, so I sent it to the clock hospital. It's back and
free-running
nicely, so maybe it's finally time I did this. Anyone got a better
idea than my
little TTL circuit, on a breadboard inside the 8170? I'd like to get
it across
the rear panel without cutting a new hole, if I can avoid it. But
maybe the
right connector would do. Another time-code receiver in the TS clock,
e.g. a GPS
module that provides a relay closure for 1 second on the hour (if
such exists)
might be neater. But the living room faces north.
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