ROM replacement options (split/OT from: WIP: MINIMON)

[srowe]

This chip goes into the ZIF socket of the MINIMON cartridge, as alternative to a 2716 EPROM.

An 8K variant of this would be very useful to replace dead BASIC and KERNAL ROMs.

(mod: topic drift split from "WIP: VIC-2020 MINIMON cartridge")

[chysn]

A new actor enters the play:

Woah, cool! Could that adapter board be used in place of a 2764? (I know that your cartridge isn't wired for that, but assuming it's put in a socket that would otherwise be occupied by a 2764...)

Edit: Oh, right, not enough pins. Question withdrawn

[Mike]

Woah, cool! Could that adapter board be used in place of a 2764? (I know that your cartridge isn't wired for that, but assuming it's put in a socket that would otherwise be occupied by a 2764...)

Edit: Oh, right, not enough pins. Question withdrawn

The AT28C64B in charge here actually *has* a capacity of 8 KB and is also available in a 28-pin DIP. I use the TSOP version for MINIMON, mainly because it nicely fits into the surrounding 24-pin DIP adapter.

The chip could also be used for a (re-)programmable cartridge, with:

/WE := VR/W (write enable) or +5 V (write protect)
/CS := /BLKx
/OE := !(CR/W & SO2)

... and of course all its address lines exposed to access the full 8 KB range.

An 8K variant of this would be very useful to replace dead BASIC and KERNAL ROMs.

Main issue when this EEPROM is supposed to replace BASIC or KERNAL: the ROM sockets do not provide a R/W line, and the /OE signal also needs special treatment during write, so you could not easily (re-)program the chip in place.

It is possible though - using an adapter/socket chain - to let the chip appear as 2364 (for the ROM socket) and as DIP AT28C64B again for a programmer. That'd require some temporary extra connections from the top adapter to the bottom adapter which are only used during programming, and are removed for normal use.

I replaced the BASIC ROM in my VIC-20 some time ago with a similar solution with a PLCC, see here. Jim Brain also offers ROM-el, which uses a bigger Flash-ROM, but otherwise works quite the same (and with the same small 24-pin DIP footprint).

Greetings,

Michael

[MCes]

I replaced ROMs with this:
http://sleepingelephant.com/ipw-web/bul ... f=3&t=9563

[Mike]

I replaced ROMs with this: [...]

For sure there exist quite some options to replace BASIC or KERNAL ROM when they're defective (or for other reasons already stated). For people who want a 24-pin DIP footprint without adapter, there's the Motorola MCM68764/66, Cypress CY7C264 or Signetics 27HC641.

With 2764/2864 or bigger (E)EPROMS and PLCC, SOIC or TSOP packages, it is possible to fit those on a adapter PCB that's just the size of the 24-pin DIP package and that's what most probably inspired srowe's remark here.

If the result is what matters, a simple 28-pin to 24-pin adapter suffices. On older VIC-20s, that makes problems though as there's not enough room between keyboard PCB and the chips to close the case.

[MCes]

If the result is what matters, a simple 28-pin to 24-pin adapter suffices. On older VIC-20s, that makes problems though as there's not enough room between keyboard PCB and the chips to close the case.

I have 27HC641 and I can flash them for who need it
http://sleepingelephant.com/ipw-web/bul ... 641#p99519

Also my other solution are not more higher than a simple chip, so also it can fit inside an VIC20 old board...
It use the same method shown into pic: