Wednesday, February 4, 2015

Card decks shared with 1130 enthusiasts, plus work on 1401 at CHM

I spent mid-day at the Computer History Museum working on a problem on one of the 1401 systems wherein reading cards on the 1402 reader will fail sporadically. There are many mechanical adjustments that are awry on the reader, but it seems that the 'read completion latch' that should be set  will sometimes fail to set, generating a second or third attempt to feed a card. Since these duplicate requests occur while the preceeding mechanical cycle in the reader is still underway, they push an all-zero card image into storage.

Right now, we see the latch failing to set with apparently valid inputs. The latch is a 'trigger' card which has six inputs - three for setting the latch and three for resetting. Each 'side' has a direct (immediate) input, plus a enabling and a rising edge input. When the enabling input is active, a transition of the edge input from off to on will activate the function (set or reset depending on side).

The scope shows the set side enable input (called a gate input by IBM) receiving a pulse, with the last of the twelve rows of the card being read showing up on the edge input (called AC input by IBM). The enable is active first, then the rising edge happens from the last card row. Most times, this sets the latch but sometimes it doesn't, causing the error. We didn't see any anomalies on the other inputs that might have disrupted the latch.

It was time for the scheduled demonstrations to the museum visitors, so we had to close up and leave it for the next time we are together. I had a bit of time in the evening to work on the 1130 project.


I began scheduling the time when I would visit a friend and read the tape on his 9 track drive. He is extra busy at this time, having a series of enhancements to make to his R2D2 for its appearance at the Maker Faire in a few months. We are still iterating to find a good date and time, but it shouldn't be too long.


The ECAP program seemed to be correct, with just a few cosmetic tweaks of the decks, so I made it available for others to download. I then went to the card file cabinet I brought back with the 1130 and began scanning in programs for sharing. Mostly it was games to run, which are likely to be a big hit with casual enthusiasts, but also some utility routines plus two math oriented programs - Complex Variables Subroutine and the Linear Programming System.

I did some verification of the reasonableness of the data capture, even tried a few on the simulator, before posting all of them via Dropbox and links to the 1130 enthusiasts.

1 comment:

  1. I would be interested in a copy of the ECAP source.


    -- glen