Electronics > Beginners
Breadboard 65c02 computer reliability/stability (er, lack thereof)
<< < (3/5) > >>
sci4me:
It was working when I went to sleep. Just got up, turned it on, and it's back to not working. Nice. Two days in a row it's done this.

So clearly I haven't even come close to eliminating all the instability...

EDIT: Slowed the clock down by a factor of two and it started working...

I'm starting to think it may be related to the USB to serial converter I'm using. It's this one: https://www.adafruit.com/product/954?gclid=Cj0KCQiAzePjBRCRARIsAGkrSm45qYTK-wOEYFku9vi1ckV7UWLs9Cgkh6FfsjBoIknZE5VU7eSxvjsaAoxqEALw_wcB

I can see that data is being written on the TxD line of the ACIA, but I also see the serial converter pulling its own Tx line low. It pulls it low a few seconds after being powered and holds it low until I power cycle it.

EDIT 2: Well I feel like an idiot. Turns out another issue I have to watch out for is my laptop assigning the USB to serial converter a different name in /dev !!

EDIT 3: Yeah I think there are power supply/distribution problems...

EDIT 4: Clock distribution? I think this is it actually. Or, part of it. I tried connecting the clock to a 74LS00 I was going to use for address decoding and it started flaking out so I undid that and it works fine again.

EDIT 5: Something about feeding the clock into a 74LS00 is definitely causing consistent instability...

EDIT 6: At this point, it will work for a short period of time and then start behaving strangely. It writes to the serial port as expected for a while and then starts missing characters and writing the wrong characters...
T3sl4co1l:
It sure would be nice to have a single ground for everything; unfortunately, the reality is that you've got a forked power distribution network, and signals routed completely away from them.  So every time a chip toggles its output pins, it produces an upset that plucks the tines like a tuning fork.

It may help to put shorting wires between grounds, and between supplies (the latter are optional if VDD/GND are bypassed to each other periodically), turning the forked power supply into more of a grid.

It would also be nice to have a connection to the ground plane, the panel the breadboards are stuck to.  Sometimes this is a bolted connection to binding posts, sometime it's completely floating.  If floating, consider scraping paint away to make a few connections from it to ground.  It's probably aluminum, so, don't expect to get a soldered connection, or at least a nice one, but a clamping spring would be okay.

High speed signals may benefit from ferrite beads, to slow the edge rate.  This would be rather annoying to employ here on so many signals, though.  I've had to do it on breadboarded SPI before, which is a lot easier to put beads on.

Tim
sci4me:
Frankly I'm quite confused as to why I'm still having dramatic instability even with a clock speed under 1KHz. Is it the edge speed, bad contacts, contact resistance, capacitance, etc.

I'm becoming more and more tempted to spin a PCB with my current design... given that I know what I've built does work. However it concerns me because I want to also add a 65c22 VIA ... and I haven't been able to test that on the breadboard. Might just give it a go, not sure...
radiolistener:
try to decrease length of wires, especially with high frequency signals.
And use exactly the same length of wires for all lines in the address/data bus.

Also, check that your power supply is enough and clean.
I noticed that these breadboard has high resistance.
So, the voltage may be drop down significantly.
When I tried to power high speed ADC through breadboard, I notice for about 0.2-0.3V drop.
amyk:
A 65C02 is a static design, clock it really slowly (as in 10s of Hz or lower) and see if your problems persist.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod