Bob,
I just looked at the clock I am not using and it is 1818-2295A, it is
not convenient for me to check the other one as it is running and in a
place where I would have to disconnect it to get it out. I could dump
this ROM for you but it may take me a few days as I have other things on
the go right now.
Paul.
On 2016-10-09 10:48 PM, Bob wrote:
Hi Tom & Paul,
Some progress with the HP 59309A clock debug. Built a ROM reader (Teensy++, a
28 pin WW socket, jumpers) and read out the HP 59309A U2 ROM.
Compared the user manual to my readings, found three stuck output bits out of
sixteen, and another few dozen assorted differences out of the 4096 ROM bits.
Also, while moving U2 to the reader socket I noticed that the chip is stamped
1818-2295A 2335 vs. the schematic which states U2 is a 1818-2193. Perhaps the
U2 state machine was updated?
The O1 (part of Next Address) bit, O9 (LOAD) bit and O11 (Rout) bit always read
0. Together those stuck-at-0 bits compose the vast majority of the bit
differences. LOAD being always zero explains why I don't see data written into
the RAM when watching with a logic analyzer.
I'm 99% sure there is at least some bit rot, in particular there is a long
unused block at the end of the Talk Enable = 1 table, where all addresses
should match, and in the middle of that range there are just a few wrong bits.
A small number of differences exist in other Next Address and Next Qualifier
columns, but there are only a few, not easy to tell if they are just changes to
the state machine or more bit rot.
Digging further, the serial number prefix 2510A is much newer than the 1632A
prefix mentioned in the manual I'm looking at, so there could be differences in
the schematic. Not clear if HP change pages up to 2510A exist, I've not found
them so far.
At this point, I can think of a few paths to take...
a) Leave it alone, still works fine as a desk clock, but useless for reading
TOD via HP-IB.
b) Build a little adapter board and replace U2 with a self-programmed 16 bit
EPROM or a pair of 8 bit EPROMs. I could use the code in the manual, buzz out
the circuit to validate the schematic, and (if needed) reverse engineer the
state machine.
Tom and/or Paul, would you consider lifting the cover off your clock (just 2
screws in the back) and peeking at the part number on your U2 chips? That's
the 28 pin ceramic ROM in the socket on the A5 board which is the one at the
far left looking from the front. The ROM is at the top of the board and should
be visible without touching anything.
If someone happens to have a ROM stamped 1818-2295A 2335, it would of course be
great to capture the bits, to remove the remaining guesswork in creating a
replacement image. Naturally, I checked the ROMs on Didier's site, but didn't
see any for the 59309A.
In conclusion, reading the U2 ROM shows three stuck bits, including LOAD, which
explains what I saw on the logic analyzer.
Cheers,
Bob
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