Building a simple 6502 microcomputer

[alkopop79]

The problem is that the pinout is different from the ones needed for the UK101. The one I have is 64K.

[Dajgoro]

The 28c64b is a 64 kilobit memory, 64K=(8K x 8 ), but it has only 8 kilobytes.
the 28c256, is a 256 kilobit chip, and it has 32 kilobytes of memory.

As for pinouts, all of this chips share the same generic pinout, and only as size increases address pins stack from the bottom up, but the rest is unchanged.

[alkopop79]

Thank you! Will purchase another one next week.

[Dajgoro]

Np.
You can probably find it in the local store, but it will be more expensive than ebay.
As for ebay, anything ordered, will arrive in January.

[alkopop79]

I found a UK seller. My only worry is programming the thing.

[Dajgoro]

If you get a free afternoon during Christmas, I could try to enter your computer via Teamviewer, and then we could take a look together on what is happening with your contraption.

[alkopop79]

Dajgoro wrote:

The 28c64b is a 64 kilobit memory, 64K=(8K x 8 ), but it has only 8 kilobytes.
the 28c256, is a 256 kilobit chip, and it has 32 kilobytes of memory.

It seems I was trying to write a 32Kb image onto an 8Kb ROM. No wonder it didn't work! However, I wrote some test-images of less than 1K and the writing/reading works perfectly with the Arduino-contraption. I only need to add an extra wire (since the address bus of the 32K ROM is 14 bit wide, not 13) and modify two lines of code. That's it. Also, it seems I have to rewire a couple of address wires on the SBC. The new EEPROM is coming this week. The uk101 was made for EPROMs which have slightly different pinout than the Atmel EEPROM I'm getting.

[GARTHWILSON]

Quote:

I only need to add an extra wire (since the address bus of the 32K ROM is 14 bit wide, not 13)

Er, make that two extra wires.
8KB --> 13 bits
16KB --> 14 bits
32KB --> 15 bits
64KB --> 16 bits

[alkopop79]

Good point, thanks!

[Dajgoro]

I am glad that it all works now. Let us know how the SBC perform when you get the new EEPROM.

[alkopop79]

Just done the NOP test and indeed, as I moved the probe from A0 to A14 the frequency gradually decreased. Gave up trying to burn the EEPROM, the contraption is not working. At least I know that the SBC will work!

[alkopop79]

Off topic: I was chatting with a fellow Hungarian friend about ROM programming. I remembered him telling a story about how his dad built an Altair clone that he eventually painted purple. I asked him where did his dad purchase Intel-stuff? At the time the West embargoed export of high tech and electronics to the countries behind the Iron Curtain (the so called 'CoCom-list'). He said, clones and black market. That also reminded me stories I read about Soviet clones of Intel microprocessors, Hungarian scientists building PDP8 reverse engineered from the manual(!), Apple I. clones manufactured in Bulgaria, East German MicroVAX II. clone, or the Polish K-202 16 bit minicomputer that competed with the Data General Supernova. Fascinating! Back to topic.

[YT2095]

if you send me the ROM Binary file, I`ll be happy to burn it onto a 27C256 for you, it won`t be a Fast ROM, but should do up to 4MHz without a problem, if that`s any help to you send me a DM

[Dajgoro]

Quote:

Gave up trying to burn the EEPROM, the contraption is not working.

Haven't you said that it worked a few posts before?

[alkopop79]

No, it's very hectic. It's driving me crazy.