I looked inside the CHI interface box and really like the idea of using five dummy PCBs in the slots to connect to the SAC cable signals. With the CHI receiver/driver cards removed, nothing touches those leads, making it safe for me to use the sockets as a connector.
|SAC signal wires are colored ones along left, connecting to backplane|
|The back side of the 160 pin socket with its colored wires in groups of 20|
|Front of the 160 pin socket|
I found prototype boards that are the right size, width, pin count and intended to plug into these sockets, but the cost for the five boards I would need will be about $130 with cheapest shipping. A second option is to use push-on terminals on the wirewrap backplane in the CHI unit but that makes it very difficult to switch back to using the CHI logic. A third option is to go ahead and by a 160 pin socket, wire up all the pins and use it on my box, which would be about $50 more. I decided to go with my own socket, making this interface easily movable to any 1130 with a SAC interface.
NEW KEYPUNCH INTERFACE DEVELOPMENT
I hammered away at the issue of reading the sense pins - the timing was an issue I had not yet resolved. After some experimentation, I found I could get a reliable read of the pins at 60ms after I involved a cycle, however what I picked up was a column too late. That is, when I do the first space I am seeing the pins corresponding to column 2. This will require some cleverness to resolve.
I also have a mismatch between the actual rows and which pins I am reading - which I believe is caused by several factors. First, I have a wiring swap to accomplish at the dup relay, where I know that the sequence of pins are incorrect compared to the DB25 cable assignment. For instance, the rows 1 to 9 are assigned to the relay contacts of the same number, while 0 is assigned to 10, row 11 is 11 and 12 is 12. This was not the sequence I used on the DB25 connector, but I corrected the wiring so everything lines up with our 'standard' keypunch wiring.
After a bit more testing, I am confident that the card reading function works well, other than the "first column" problem. I read cards successfully in both ASCII and BINARY modes. I haven't tested the 'verify after punching' mode yet but that shouldn't be too bad since it mostly uses existing and debugged logic.
I checked to see whether I could see the hole pattern when the card is registered in the read station but before I punch the first space, but that doesn't work. My proposed solution is to use the multipunch feature to punch a space, assuming the keypunch can handle this mixed signal, then drop the multipunch key and issue the space again. That way I might read the initial column while in multipunch mode and get the second column as part of the first real space.
I do have to experiment to see if this can work - testing the logic of multipunching a space but also seeing if the escapement occurs immediately, moving me past column 1 on the read station. If it moves first, I will need a plan B and I don't have a clue right now about how I might address the issue.
SAC INTERFACE FOR ADDING PERIPHERALS TO THE 1130
I completed testing of all the circuits on the four boards, which helped me find two solder bridges and one resistor lead that wasn't soldered down. I then made the decision to buy a 160 pin socket, wire up all the pins and use it on my box. Ignoring the socket on the CHI interface and using my own makes this interface easily movable to any 1130 with a SAC interface.
|My testbed to verify the circuits worked properly|