"D7" stuck at 0....W (write) LED never blinks.

[wa6vpl]

Nice kit Nicola! The board appears to be working as designed, However, I am having a problem I need some help to fix....
Not able to see an output at OUT0. Analysis with O-scope and logic analyzer revealed "D7" out of the RAM is stuck at Logic 0 and the W (write) LED never blinks. Looking at the load at power-on (plugging in USB) revealed no transitions on D7. Then I removed the Nano and connected Logic Analyzer to the appropriate pins to trace: PRG, WEN, D7, D6 and GND. D6 looked OK but D7 did not toggle at all during the boot. Is this a defective Nano? I have a Rev C. board...tried to figure out from your Github site if there was something not in sync. I suppose a simple program could be tried to toggle pin12 (D9) to see if "D7" is really stuck...but I am unsure if I have the smarts to reload the monitor.
Any ideas where to look? Thanks, Jim

[nicolacimmino]

Hi and thanks!

REV.C is good, it's the latest and actually what the vast majority of kits have been shipped with.

The 14500Mon is simply an Arduino sketch (it includes both the bootloader and monitor functionality), so as long as you have an Arduino IDE you should be able to load it. ( https://github.com/nicolacimmino/PLC-14500/tree/master/14500mon )

It seems like it could be the Nano. If you have a spare one perhaps you could try to load there the 14500Mon.

I'm travelling at the moment for 2 weeks, but PM me if you like I can send you a spare one on my return.

[wa6vpl]

Thanks for quick reply. I am familiar with using latest IDE and programming other types of boards (Uno and Mega). So will give it a try and let you know results. I do not have any spare Nano's, so will be very careful checking pins and running test sketch.

_____ From: Nicola Cimmino ***@***.*** Sent: Friday, July 14, 2023 12:30 AM To: nicolacimmino/PLC-14500 Cc: wa6vpl; Author Subject: Re: [nicolacimmino/PLC-14500] "D7" stuck at 0....W (write) LED never blinks. (Issue #9) Hi and thanks! REV.C is good, it's the latest and actually what the vast majority of kits have been shipped with. The 14500Mon is simply an Arduino sketch (it includes both the bootloader and monitor functionality), so as long as you have an Arduino IDE you should be able to load it. ( https://github.com/nicolacimmino/PLC-14500/tree/master/14500mon ) It seems like it could be the Nano. If you have a spare one perhaps you could try to load there the 14500Mon. I'm travelling at the moment for 2 weeks, but PM me if you like I can send you a spare one on my return. - Reply to this email directly, view <#9 (comment)

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[wa6vpl]

I was wrong with saying I could not get things working. Everything is just fine. I was not using the assembler correctly thus the in and out ports were not letting me set the Result Register. It paid, for me at least, to read as much of the documentation as possible on your Git Hub. I should have looked closer at the schematic to determine each port's address. I needed to turn the board around 180 degrees so that the LSBs were to the right. That makes it easier (for me) to read the program counter, op code and port address when single stepping. This will date me perhaps. Going back to the late 1970's my early 8080 and Z80 kit computers had lots of LEDs and toggle switches on the front panels that were set up for LSB starting from the right side. Thanks again for a great design. My time revisting the old computer hardware for the last couple of years brings back great memories of when I was a development engineer working on process control sysems for nuclear power plants. Regards, Jim Hi and thanks! REV.C is good, it's the latest and actually what the vast majority of kits have been shipped with. The 14500Mon is simply an Arduino sketch (it includes both the bootloader and monitor functionality), so as long as you have an Arduino IDE you should be able to load it. ( https://github.com/nicolacimmino/PLC-14500/tree/master/14500mon ) It seems like it could be the Nano. If you have a spare one perhaps you could try to load there the 14500Mon. I'm travelling at the moment for 2 weeks, but PM me if you like I can send you a spare one on my return. - Reply to this email directly, view <#9 (comment)

it on GitHub, or unsubscribe

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[nicolacimmino]

Good to hear all is working!

I had some others mentioning the bit order on the board LEDs. TBH given it's a 1-bit system I always thought of them as independent I/Os, but true that when it comes to the address bus expecially one expects to read it as a number. I currently have a quantity of boards sitting under my desk, but when I will run low I could consider flipping, with some more tweaks.

You mention revisiting old computer hardware, I am on the lookuout for ideas for a new retro kit, any thoughts on what might be cool?

[wa6vpl]

Nicola, If you make another rev/run of your 14500 design, I thought a simple I/O header for off-board control of something....like a relay board or opto-isolator input. On my 14500 wire-wrapped prototype, I did just that. I've also been going through the Z80 / Z180 retro computing thing. Steve Cousins' kits and the RC2014 kits are fun to build...and re-learn machine coding and Basic again. My very first job out of college in 1975 got me into imbeded processing circuit design and machine coding. I prototyped a 6800, but soon we moved on to the Z80 for a safety control system for Nuclear Power Stations. I never went back to working with the Motorola 6800 or any of its varients. Anyway, today in retirement I have acquired 2 of the Heathkit ET-3400 microprocessor trainers. They have a monitor in ROM and there is an upgrade box for a Tiny Basic in another ROM. One of my ET3400's was so damaged that I could not get it to boot up with the initial display: "CPU RDY". There are water damaged traces and corrosion under a number of IC sockets. I fixed some of them but the board, overall, was trash. So....keeping with the "Motorola" theme..... I thought I might take the design and make my own copy...change the RAM from 2114's to something a little more modern and reuse the ROM for the monitor. There is also MikBug and other homebrew monitors out there too. Now, if there were a kit using the Motorola 6802/6808 processor and a boot loader for loading and saving code (similar to your 14500 kit).....that would be an interesting retro computing kit. I could send you a PDF copy of the orginal Heathkit schematic if you are interested. Regards, Jim Good to hear all is working! I had some others mentioning the bit order on the board LEDs. TBH given it's a 1-bit system I always thought of them as independent I/Os, but true that when it comes to the address bus expecially one expects to read it as a number. I currently have a quantity of boards sitting under my desk, but when I will run low I could consider flipping, with some more tweaks. You mention revisiting old computer hardware, I am on the lookuout for ideas for a new retro kit, any thoughts on what might be cool? - Reply to this email directly, view <#9 (comment)

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[nicolacimmino]

Hi,

thanks for your message. A I/O header on the PLC14500 is a great idea indeed, I'll keep that in mind!

That Heathkit ET-3400 sounds really interesting, I have just taken a look at it now, was not aware. If you could send the schematics or anything you have that would be great! You can mail me at nicola.cimmino@gmail.com

Nicola