Mystery IC: Allen Bradley 314B102

[Mike Ross]

On Wed, Dec 16, 2015 at 8:01 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
> On 2015-Dec-15, at 6:21 PM, Mike Ross wrote:
>> On Wed, Dec 16, 2015 at 11:43 AM, Mike Stein <mhs.stein at gmail.com> wrote:
>>
>> I have taken Brent up on that :-)
>>
>> I'll poke a bit more myself and see what we can work out together
>> before I decide if the effort is worth it.
>
>
> First crack can be picked up here:
>         http://www.cs.ubc.ca/~hilpert/tmp/WIOSelectric.pdf
>
> There are a few areas and pins I couldn't discern from the photos.
> Mostly around U1 & U6 as the lens angle and lighting is hiding some connections around those.
> If you take another photo or check some of the connections marked in red I can update the schematic.
>
> I've labeled the host interface connections as per the most likely scenario:
>         D0-D6: in correspondence to the 'normal' PROM addressing, so D0 is likely the ASCII LSB.
>         nSTB: this should be the print-strobe input, looks like active-low.
>         BUSY/RDY: haven't examined the logic enough to say whether this active-high or -low for whichever way one chooses to interpret it - BUSY / READY / ACK.

Amazing work Brent!

I've wired the thing up in accordance with your schematics and here
are the results:

On power-up the line we believe is Strobe is high; all others are low
- and I'm monitoring the printer side of the interface here.

I cat file.name > /dev/lp0

The printer prints a character; Linux is waiting. The line we presume
to be Busy/Ready flickers briefly high as it is printed.

I toggle the local/com switch from com to local and back to com:
another character is printed. Linux waits. I can sometimes continue
this process one character at a time by toggling the local/com switch.
At other times toggling the switch sends Linux straight back to the
command prompt.

The characters printed are pretty exclusively semicolons underscores and 8s.

The carriage never advances; all characters are printed at the same spot.

Further observations:

- If I initiate the print with the Strobe line disconnected Linux
returns to the command prompt instantly and nothing is printed.
- If I disconnect the Strobe line after printing has started Linux
returns to the command prompt instantly after the com/local switch is
cycled
- If I disconnect the Busy line prior to starting to print nothing is
printed until I connect the Busy line
- If I print a character by cycling the local/com switch with the Busy
line disconnected a *second* character is printed when I reconnect it.
- Busy flickers high every time a character is printed. The status of
the Strobe line never visibly changes; it always appears high. Might
put a scope on those...

There's clearly something funky going on with signaling - timing or
active high vs. active low. At no time does the printer *ever* print
more than one character without some manual intervention.

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