Building a simple 6502 microcomputer

[8BIT]

alkopop79 wrote:

Just found an article about how to program EEPROMs manually. I also saw a DIY circuit somewhere for this task. What's your angle on this guys? EEPROM or EPROM?

Hi alkopop79,

I for one prefer the EEPROM's as they do not require anything special to program. They also do not need a special UV light to erase and can be re-written a byte at a time if you want to.

When I built SBC-1 (a long time ago), a created a home-made programmer that used the 8 bit data lines of a PC parallel port, feeding 74373 latches to hold the address and data values while driving the /WR pin from a status pin. I use QuickBASIC in DOS 6 to drive the port and program the EEPROM.

I later built an EEPROM programmer driven from a 6522 VIA and programmed using 65c02 code. it can be found here: http://sbc.rictor.org/28256.html

About 10 years ago, I bought a serial port driven programmer from EBAY for about $50. It has served me well for programming 32kx8 EEPROM's for all of the SBC-2 & SBC-3 boards that I have created.

Feel from to ask me any questions about doing any of this yourself.

Good luck with your project.

Daryl

[alkopop79]

8BIT wrote:

alkopop79 wrote:

Just found an article about how to program EEPROMs manually. I also saw a DIY circuit somewhere for this task. What's your angle on this guys? EEPROM or EPROM?

Hi alkopop79,

I for one prefer the EEPROM's as they do not require anything special to program. They also do not need a special UV light to erase and can be re-written a byte at a time if you want to.

When I built SBC-1 (a long time ago), a created a home-made programmer that used the 8 bit data lines of a PC parallel port, feeding 74373 latches to hold the address and data values while driving the /WR pin from a status pin. I use QuickBASIC in DOS 6 to drive the port and program the EEPROM.

I later built an EEPROM programmer driven from a 6522 VIA and programmed using 65c02 code. it can be found here: http://sbc.rictor.org/28256.html

About 10 years ago, I bought a serial port driven programmer from EBAY for about $50. It has served me well for programming 32kx8 EEPROM's for all of the SBC-2 & SBC-3 boards that I have created.

Feel from to ask me any questions about doing any of this yourself.

Good luck with your project.

Daryl

Amazing stuff, thanks Daryl!

[alkopop79]

Toying with the idea of using an Arduino as an EEPROM programmer. This chap used a Mega:

http://z80dave.blogspot.co.uk/2011/09/2 ... ammer.html

The only thing that worries me is the software. I don't really understand how the software works. I guess I could write something in Java or Python but don't know the protocol.

[alkopop79]

I compiled a list of components and they're ready to be ordered once I get some dough. The only thing I could not find is the wire wrapping board. Any ideas where can I buy one? The ones on ebay sell for hundreds of dollars...

[alkopop79]

Also, is there a replacement for the 28256 EEPROM? They're discontinued and sold on ebay for vintage IC prices. No big deal but would rather spend money on something that's supported and brand new.

[alkopop79]

The shipping form the US costs twice as much as the 28256 itself...

[Arlet]

alkopop79 wrote:

Also, is there a replacement for the 28256 EEPROM? They're discontinued and sold on ebay for vintage IC prices. No big deal but would rather spend money on something that's supported and brand new.

Try the AT28C256. If you don't need 32KB, you can also get a AT28C64 (8KB) for half the price.

[alkopop79]

Great, just found it! Both RS Online and Mouser stock it. The ebay ones are outrageously expensive... Thank you, Arlet!

[BigEd]

I found this note in http://www.timefracture.org/D16docs/wire_wrap.html:
"For small projects (smaller than 30 IC’s, say), I just install wire-wrap sockets on a perforated board"
and also "Decent wire-wrap IC sockets are costly (in general, they will cost more than the IC’s they support!), but they are essential for reliability. "

For memory, you might consider battery-backed SRAM, either DIY or as a module. See this earlier thread:
viewtopic.php?p=16905#p16905
(but I see we have an affordable EEPROM option now!)

[Arlet]

You can find a lot of this stuff using the distributor's on-line parametrized catalog. Look for EEPROM, select 'parallel' option, select DIP package (if required), size, and it will show a list of matching parts. When you've narrowed down your search, sort by price.

[Dajgoro]

Vintage eproms and eeproms tend to be slow, just watch that they aren't too slow, but i guess it will work fine for you. I use eproms only when large amounts of data need to be stored, since there are cheap eproms that reach up to 1MB.
As for eeproms i just bought another 28C256 for my new cpu board that should replace my sbc board, and there is also a good trick about the 28C256, since it is 32k, and i only use 16k, you can fit 2 programs in your sbc (two systems).
And also try to get a zif socket for the eeprom, it will save you lots of time, and it won't damage the pins when you pull it in and out.

[alkopop79]

Where can I find wire wrap board? Can I just use a perf board instead?

[BigEd]

(see my previous post!)

[alkopop79]

Thanks, indeed! How do you 'fix' the sockets to the perfboard? Can they be soldered to the board?

[BigEd]

got me there - hot glue? Or maybe they push-fit.