Sunday, February 1, 2015

Testing of card reader interface, plus minor work on other fronts


I tried out a variant suggested by a blog viewer, putting the equivalent of the ruler as a new short line at the top of the status pane. If I like the way it looks and acts, I can strip out the menu command for a ruler, since this could operate at all times. I will do most of the coding and testing tonight once it is too dark to work on the card reader interface.


Got out this morning and wrapped up the wiring of the card reader interface to the Documation. Right after, I inserted the three chips, hooked up power and was ready to program the microcontroller. In order to do that, I had some prep work on a PC.

I installed the software necessary to program the Parallax SX microcontroller, got the SX Key controller board recognized by the PC, and opened the program written by Brian Knittel. Once everything looked good, it was time to plug in the SX key to the circuit I built, power it up, and download the microprogram.

In addition to installing code in the microcontroller, there is a PC side program that Brian wrote which communicates over USB to the interface in order to control the reader and capture cards as they are read. The USB interface drivers and the program were installed.

Time to test this all out! I brought up the Documation reader, the interface box and the Surface Pro tablet running the PC program. I had a problem with the wiring to my SX-Key programming header, putting ground on the wrong pin, which gave me an obscure error "Unable to generate Vpp" but once I fixed it, I could program the microcontroller and verify its proper contents.

The next challenge was communicating between the Cardread.exe program and the interface box - the PC side program complained about problems with COM3. I needed to look into the code to see whether there was a dependency on a specific serial port or a configuration option I missed to set it properly.

With that process completed, the program was successfully exchanging messages with the interface box, which itself was able to see the hopper empty state correctly. However, when it tried to pick cards to start reading, nothing happened. I suspect that the modifications I created, for my IBM 1130 system replica and the interface box that would make it appear to be an IBM 2501 reader, were at fault here. I had changes wired into the reset function and remote activation of the stop button, both of which could cause the reader to sit idly.

I went over my documentation of the modifications and discovered that I had only to remove the connector I had added to the back of the Documation and it would be capable of operating normally. However, the reader still didn't pick cards. I saw the program flickering the "pick pending" message but nothing was occurring on the card reader.

I made the rash assumption things were sensing properly because it detected the state of the hopper, but when I looked at the schematic I noticed that this was the only card reader signal that went directly to the SX microcontroller. The rest went into the 82C55A peripheral interface chip (PIA),

I put the scope on the interface and immediately saw that the PIA chip was not driving the pick signal to the 7426. The chip does have +5 and ground, so my debugging will need to be a bit more detailed. I also threw the VOM on the reset signal, finding it sitting down at 0 as it should.

At this point, I will have to start scoping and measuring voltages on the various pins to see if I can sort out the error. I will make a quick check through my parts bin tomorrow to see if I have a spare 82C55A which I could swap - the advantage of using sockets instead of direct soldering is clear.

I did spot a wiring error, with the two address lines swapped between the SX28 and the PIA. I correct the issue, but there is still something else wrong. I checked for shorts and traced wiring several times, but missed this problem; as a result, I have to assume an additional miss-wiring exists that is causing incorrect behavior. The light has faded, however, and my workday is over.


I am expecting a mag tape which has some source code on it related to 1130/1800 systems. The owner offered it up for reading, to share anything interesting we find on it. When it arrives, I will arrange some time on a system with a 9 track drive and get the data extracted to the degree possible with old media.


Now that the degree of distortion of the shed has been reduced a bit, it is time to try the wood shims that the kit maker suggests as the means to adjust the door alignment. However, the shed does seem to have gradually twisted itself back to perhaps half of the original misalignment.

I can shut the doors and open them, although they look ugly with the significant misalignment, which does create a minimum acceptable level for using the shed. As such, I will work on improving the alignment as a cosmetics project but may leave it for long stretches if it is too balky, meanwhile I will outfit the shed and begin using it.

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