I think I found out the issue. It was in the hardware, but not a fault in my wiring, a bad solder joint that had gotten loose, or in the design itself.

Part of the address decoding for the SRAM is a diode logic OR-gate. I thought that perhaps the slower fall/rise times of diode logic was causing ...

$0000 - $03ff On-board RAM
; $8000 - $9fff Video RAM
; $a000 - $afff CRTC
; $b000 - $bfff PIA
; $c000 - $ffff ROM

PIA_PORT_A = $b000
PIA_CONTR_REG_A = $b001
PIA_PORT_B = $b002
PIA_CONTR_REG_B = $b003
CRTC_ADDR_REG = $a000
CRTC_DATA_REG = $a001

.org $8000
.org $c000
reset:
sei
cld

ldx #$ff ...

Might we perhaps see the listing for the compiled code? I note that there is neither an .org statement in what you've shown, nor a stack setting instruction. I wonder if your code is being assembled in such a way that its thumping the stack?
Here's both the full assembly program as well as a ...

Might we perhaps see the listing for the compiled code? I note that there is neither an .org statement in what you've shown, nor a stack setting instruction.
I do have orgs in the "full" assembly. A tiny bit foolish not to include them but I can say for sure that the program starts at the correct ...

Yesterday night I was trying to write a subroutine to set the registers of an MC6845. I haven't spent much time at all working on software for the 65C02, but I have written
subroutines in the past and I have the feeling that I shouldn't be having so much trouble with such a simple thing.
My first ...

But again there's nothing wrong with using buffers, since you're already doing that for the 6845 - you just need to use them between the 6502's address bus and the video RAM's address bus.

The extra buffers make sense now that I think about it. I was hoping I would be able to save a few sockets ...

I recently got an MC6845, and I have been able to produce a screen-full of text. My test setup has the data bus connected to an Arduino, the 6845's address bus simply going to an 8K SRAM, the
character clock at 1MHz, and pixels output at 8MHz. The 6845 is programmed to provide a 50hz VSync, and has ...

I've got good news, and good news only. It really was the LCD!
I read the datasheet for the LCD's control chip and it specified a minimum enable pulse of 450ns, so I assumed it wasn't the problem since it couldn't run even at 500KHz. I gave the datasheet another look this morning and found that the ...

Although I've just checked the schematic you linked to - the LCD is directly connected to the bus - it's possible that the LCD simply isn't fast enough. They're really not designed for high speed, so check the timings of the particular one you have. I've always connected them up through a VIA.
I ...

My second/latest 65C02 computer, constructed on stripboard around February this year, was built to run at 1Mhz. I didn't take bypass capacitors particularly seriously at the time and had even less knowledge about electrical performance than I do now- I thought that it being a soldered design would ...