SBC-85 Bus Monitor Supreme

Received a fresh shipment of boards from PCB house a couple of days ago and among them was version 1.1 of the bus monitor supreme.  I have pretty much assembled everything and am well into the testing phase.  All the issues that i wanted to correct from version 1.0 seem to have been corrected OK, except one capacitor that I had added to make the single step reset signal more robust.  Fortunately, I was able to depopulate and save all of the LEDs and nearly all the capacitors and other pricey items.  However, in the desoldering we lost the momentary single step push-button so I need to get another one on order.

I really like having both the hexadecimal and binary display of the address and data.  I also really like the machine cycle type filter, it is impressive to see it jump from memory write to write, read to read, and so forth.  Heck, I think I like everything so far about this bus monitor.

If everything continues to go well with the testing, I will release this version of the build files on the SBC-85.COM project site.

I don't wirewrap anything anymore, so i go directly to a PCB.  The prototype PCB was received in January and has been built.  I messed up the placement of some of the LEDs and didn't like the way the single step reset would occasionally miss a button press or it would take two presses to get the step to advance.  The guy that sold me the decoders for the 7-segment displays sent the wrong part (shipped surface from overseas) so I was out another 5-6 weeks waiting for the correct component to arrive.  Rather than finish the build of this board, I decided to go ahead and make the revisions I wanted and get version 1.1 on order.  Since the decoders are coming surface and the PCBs by express, they both should be arriving before the end of March.

On version 1.1. of the layout I fixed the LED placement and did a little modification to the reset logic to make the step reset more reliable.  There were also a few LEDs that kept confusing me, like the "pulse train" LED which was meant to show the user how quickly the step pulse train is but it is always blinked even if the board is not in the automatic 'slow step'. Since this caught me off-guard a few times (thinking it should be stepping when it was actually in manual step) so I changed that LED to reflect when the 'step' command is given either by a button press or by the pulse train.  There were a couple other changes to the LEDs along those lines, hopefully to more clearly describe the board condition at a glance.

The biggest thing I changed in v1.1 is swapping out the bus type filter BCD rotary encoder for the complement output version.  In the original design I was fighting the natural input pull-ups of the logic devices with pull down resistors of my own connected to the encoder.  I knew better, but I decided to go that route because I already had the switch.  Mistake made, lesson learned.  While it worked OK, the signal levels were nothing to be proud of so in v1.1 I switched all the logic so the pull resistors were now going in the direction the signal wanted to go anyway.  So much for saving $5 by using a switch I happened to already have.