Hi Steve,

Unless I'm missing something, it looks like RAMOE is just the inverse of ROMOE. If that is true, then RAMOE is low for $0000-$DFFF. Your IO is also low during $D000-$DFFF. This may be why your IO reads are not working. RAMOE needs to be from $0000 to $CFFF only.

Daryl
This makes ...

I forgot the memory map.

$E000-$FFFF ROM
$D000-$DFFF IO

Everything else is RAM. I have a bunch of nice UM61512's that are fast and work great.

Steve

In my POC units, I use a DS1813 to debounce /NMI. The firmware intercepts the NMI and if it is generated while the MPU was running a RAM-based program, the program will be interrupted and the M/L monitor will take control. It’s a handy way to break a runaway loop without losing the environment ...

Thanks for all of the replies...
This doesn’t directly relate to the problem you are having, but what is debouncing the NMI push button?

I should mention that posting a fragment of the schematic is not usually helpful for others trying to help you debug. Let’s see the whole enchilada.

It isn't ...

Thanks for all of the replies! I grabbed the relevant part of the schematic and made it greyscale.

I've set bit 0 to SCLK, bit 1 to MISO, bit 2 to CS, and bit 7 to MOSI.
Is this just a error in writing the post? Your code wants bit 7 to be MISO (master- in / slave- out ), not MOSI.

Edit: See ...

Good afternoon!

I've finally gotten back to building 6502 SBCs. I've run into an issue that is boggling my mind. I've been trying to fix it for two weeks and I've been losing sleep.

My current design uses a WDC 6522 to bit-bang SPI to a MAX3100 UART. I've had this working without issue in the past ...

On a lark I just pulled out the LCD. Board ran for 6 hours with no issues. Remember, there is no code driving it now, it's just in the circuit connected to the 6522 but I don't make any usage of the 6522 at all. I put in a 10MHz can, and it's been running now for a couple of hours. 10MHz has never ...

I've been experimenting trying to find the source of the crashing. There were some interesting developments.

I was running the SBC at 6MHz, and it would crash around the 10 minute mark. I switched to a 1MHz can and it crashed after an hour. Of course I thought this meant perhaps there was some bug ...

Hello again all!

I've made some changes that someone may find interesting. Slightly. Well, not really.

This new logic will allow you to place the IO page anywhere on the map. I've tested it at $FE00 and $0000 and it works. I wonder if there's an application where having IO on zero page would be ...

It's alive! There must've been either a bad connection or a crossed connection. It works now. I'm running my LED loop test except I changed it to store the $55 value to $C000 and $AA to $7000 so as to test each side of the 32k threshold. It's been running for about 5 minutes without issue now. I've ...

Have you separately confirmed that the IO space works? It seems to me that your 55/AA /FE test with ram doesn't exclude the possibility that IO could be flaky (too). I mean it's technically possible just from that test that IO is a problem.
I did a bunch of tests with the 6522 and some LEDs that ...

Can I just point out that some members here have difficulty reading coloured schematics. It would be appreciated if you can either post black and white diagrams, or provide both.

Also that there is normally no problem with 74HCxxx driving 74HCTxxx. And there is no problem with 74HCTxxx driving ...

We're not gonna judge your project in terms of a beauty contest -- this is about functionality. We've doled out advice to project builders before, and it's by no means uncommon that a photo will reveal crucial details which the builder overlooked or considered unimportant.
I'll do a before and ...

Thanks for noticing my mistake with the resistor network. That's a PCB component, the breadboard has some individual 3.3k's tied high. All of the gates not used are also tied high.

I think I'm going to rewire the board (BB830's) and I'll use busboard's jumper wires as well. Hopefully I'll be able ...

Thanks for the tips!

I have connected both CS and one input of the AND to PHI2 as recommended. I've also added some more 100nf capacitors. I connected 8 LEDs to port A of my 6522 and have done some testing, and I'm getting some rather odd behaviour.


main:
lda #$55
sta $0000
ldx $0000
stx ...