Hey, thanks for the responses!


My RS-232 primer has a few paragraphs about 30% of the way down the page about a bug in the WDC W65C51N, discovered by forum member floobydust (who posted above while I was writing), in that the transmit-register-empty bit is stuck in the "on" state, meaning you can ...

Hey, thanks for the responses!


My RS-232 primer has a few paragraphs about 30% of the way down the page about a bug in the WDC W65C51N, discovered by forum member floobydust (who posted above while I was writing), in that the transmit-register-empty bit is stuck in the "on" state, meaning you can ...

Hey all!
This is my second attempt at building a 6502 based computer. My last attempt was not very succesful so I still consider myself very much a newby.

At the moment my computer consists of a 65c02 CPU, 32k ROM (AT28C256) and a 6551 ACIA.
I am using the memory map recommended in the primer found ...

These three accesses are writes, and according to the code they are the correct adress and value, so everything is as expected.

Btw, I included the monitor, and the port of ehBASIC im using.

Oops, sorry for missing that.

So the first time the acia is selected, is on adress $8801, the data lines then read: $00
A couple cycles later it is accesed again, this time on $8802, and on the data lines: $0B
Then a few cycles later it is accesed again, this time on $8803, giving me $1E on the ...

Update:
I have replaced the 1,8432 crystal with an oscillator module, so that works now...

I also managed to find an error in the adress decoding logic going to the 6551, which I have now fixed, so it is'nt being accesed at the same time as the rom anymore.

Fixing this mistake made it so now ...

So normally my clock runs at 1 MHz, and I have a 1,8432 MHz crystal for the acia.
I suspect however that the acia crystal is not operating as it should, this may also be the cause for my problems I think.

As for the single-stepping method, I just step the clock. Would using RDY be better or easier ...

Ok, so I ran the test you suggested.
When I first did the test, it did not look like I was getting the right data, or even adresses.
Instead of fetching the high and low byte from FFFC and FFFD, the processor was looking at FFFE and FFFF.

But then I removed the ACIA (I am using the R6551AP) and ...

Aah, that would explain why my 6502 was acting up. I thought it was broken, because when I tested it with a 65c02 chip I have, it did work..
As for using a 65c02, would I need to make changes to the code if it was originally written for a 6502, and would I need to reassemble the code ?

I have not modified the schematic, I have just swapped out the eeprom I had, with a bigger one. they both have the same pins, just a different layout.

I had already made a single stepping device out of my arduino.
Using this I first tried using the rom image from the symon examples, and single ...

So I have looked into how the addres decoding works. This way I made a block diagram of my memory map. I feel like I have a better understanding of it now.
I also found out I have a 256k eeprom laying around, so I replaced my 8k one, and ran another NOP test just to verify I did everything correctly ...

Then what would happen if I used a ROM chip bigger than 16k ?
Would then only the first 16k of the chip be available, or what would happen ?

Well, the ROM chip Im using is only 8k, and it starts at C000 like you said.
That leaves me with only two options to correclt allign the reset vector the start of my code, right ?
I either need to change the wiring, so the ROM starts at DFF8.
Or I have to buy a 16k EEPROM to replace my 8k one.

My next question would be, where do I put this on my ROM chip, at the beginning, or the end ? Because when I look at other preassembled images I find the ROM at the bottom.

I figured it out, well not really, I just just the windows executable files and dragged the min_mon.asm file over it, and it worked. After this I could just use the second command without problems !