Monday, September 7, 2015

Console Printer looks very good and the enhanced functionality of the SAC Interface box is working well


My wife is decorating a fundraiser for a local foundation, an Italy-themed outdoor event, and has built roman columns, venetian mooring poles and many other items, but turned to me to help build a gondola in which arriving guests will pose for pictures. My son-in-law will be dressed in an authentic costume as a gondolier, with his pole at the ready. Blue tule will make the water underneath.

The gondola will be 16 foot long, with a 3 foot wide bench for guests, and the ends will stand about 4.5 feet tall. Mostly made with 1/4" plywood, the bench out of pine, and various pine sticks to reinforce the sides and bow them out to a pleasing angle. Will be painted black, with silver ends and various decorative touches along the edges.

It may be too darned hot to subject the 1130 to power, but clearly not too hot to be sawing, gluing, drilling, screwing, and so forth out in the sunny backyard. I was cooked by dinnertime.


While I had the 1130 powered up, I did some testing of the tab, space and return buttons, which did seem to be working pretty reliably. I still need to run diagnostics to be sure that the 1053 is solid, but it is getting too hot right now to subject the 1130 to any more power-on time. I will continue in the evening when it has cooled down.

I fiddled around with the overly delicate and unreliable wiring on SAC Interface Box driver board, until bit 12 was working properly. I loaded and verified the diagnostic for the keyboard and console printer, then began running it to test out the 1053.

Things looked very good - using the keyboard to printer test I was able to verify that space, backspace, and tab worked properly. When it attempted a carrier return, the stiff pivot arm did the expected and left the mechanism hung up so that it wouldn't type any more. Letters look very good and the operation is pretty solid as far as I got it.

I had to power cycle the machine to overcome the hung up state of the adapter, then decided to reload the diagnostics into memory so that there was no residual state in the software that might cause problems. Alas, while I was doing this, I decided to clean up the area and put away a VOM. Unfortunately, one of leads brushed every so lightly across some cabling in the SAC box, which caused bit 12 of the incoming data to again go missing.

I couldn't do any more testing, at least until I find and fix the problem wire for bit 12. However, I was very, very encouraged by what I saw so far. I want to run through the entire diagnostic suite and check off everything on the console printer. I will turn my attention to wiring up the three 1130 control panel buttons to the relay board so that my software can cause a virtual Program Load operation, which burns up some time until the new connectors come (see below) and I can be done with these frustrating connectivity problems.


My test of the enhanced functionality, providing control over interrupt levels 0 and 1, worked perfectly! I can trigger and observe both interrupts at will. That proves my daughter card and the DC-DC power converter are working as intended.

I wired in the trigger for the virtual Prog Load as that is the next function to test, watching the relays trigger, before I make the change to wire the relay board in to the 1131 button circuits. This too worked perfectly, the PC program commanded the sequence and I watched the relay board cycle through exactly once any time it was requested.

There is the remaining problem from yesterday that somehow the Interrupt Level 4 request is hot - that needed to be traced down and fixed before I continued testing. I remain deeply unhappy about the connection method for the twisted pair ribbon cable to my driver card inside the SAC interface box.

Currently, I have header pins on the board and attempted to solder the multistrand wires from the ribbon cable to each pin. This doesn't work well - I end up with stray wisps, connections that seem soldered by which will rotate and make intermittent contact. Sometimes adjacent wires touch.

I need a much more reliable connection method, consistent with the existing board which alternates input and output pins on the DIP chips. I choose a 2 x 8 IDC header to fit on the board and solder down, with a ribbon cable connector. I can fan out the ribbon cable wires I want and solder them to the existing ribbon cable wires, this gives me the alternation and spacing I need. These are on order and should arrive by the tail end of the week.

I looked carefully but didn't see any loose or shorted wires on the output board that would account for the undesired trigger of Interrupt Level 4. Putting on a voltmeter showed me that the output from the fpga to the chip input was invalid. It was sitting at 1.5V but should have been either near 0 or 3.3V.

That seems like a voltage divider, which might occur if two signals were shorted, one at 3.3 and one at 0, but I don't see any spot that is shorting. Similarly, this can be the result of the fpga circuit entering a metastable state, neither 0 nor 1.

I lifted the line from the chip and measured it - it still went to 1.5V which means either a problem on the fpga board, a problem in the connector or a problem in the ribbon cable. I pulled the ribbon cable off the fpga board and inserted a single pin into C12, the port where I am seeing this problem. The result was a nice low signal at level 0, as it should be.

I did some continuity testing between that wire and adjacent wires, but no shorts or measurable resistance. No short to ground. It is odd, because it is acting like an undriven pin yet I can see the source being set in my VHDL and the constraints file seems correct for the pin as well. This is odd because this used to work until I made the latest round of changes.

I did have some completely unrelated pins hooked to an Arduino from when I was testing the medium speed link, with no power applied to the Arduino but its ground was not tied to the SAC box. I removed the four wires to the Arduino and my problem with Int Req Lvl 4 went away! However, in all the moving of the board to check for problems with the request line, I managed to jostle the line for bit 12 so that it was no longer working. Grrrrr. The new connectors can't come soon enough - this unreliability of the lines is really wasting time. 

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