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Chromedome45
December 8th, 2011, 04:24 PM
Can the original Macintosh 128 use standard EPROM's? I was thinking of doing a ROM update to support 800k Drives but can't find any info about the original ROM's used in this computer. I need to know the pinouts to be precise. So Could say a 27C256 EPROM be used?

Chromedome45
December 9th, 2011, 09:12 AM
What, no one has tried doing this?

olePigeon
December 9th, 2011, 09:36 AM
I have no idea. I know that the Mac IIci can, if that helps.

RWallmow
December 9th, 2011, 11:52 AM
I do not believe it can support the larger EEPROM size that the Plus ROMs require, I want to say the 128k and 512k were a 64KB ROM, to the plus's 128KB ROM, and were never designed to read a 128KB rom, be it ROM or EEPROM.

dorkbert
December 9th, 2011, 12:19 PM
If memory serves, the the only difference between Mac 512k and 512ke was the ROM; the former had 64k ROM and the latter had 128K ROM, on identical logic boards. The Dove MacSnap SCSI upgrade for the 512k requires 128k ROM to be able to boot from SCSI. Don't know about the 128k boards.

Chromedome45
December 9th, 2011, 12:33 PM
I think my post is confusing. What I am trying to find is the pin outs for the ROM's used in the orginal 128k Mac. I know the ones I have were made by Synertek but can't find any info. Like I said just looking for pin outs of the chips. I hope this clears things up a bit.

bluethunder
December 9th, 2011, 07:19 PM
This might help..

http://68kmla.org/forums/viewtopic.php?f=7&t=16010&p=151894&hilit=mac+eprom#p151894
http://68kmla.org/forums/viewtopic.php?f=7&t=14850&p=142219&hilit=128ke#p142219

dorkbert
December 9th, 2011, 08:27 PM
To support 800k floppy drives, you need 128k ROM (27C512 x 2) and they should just drop in and work.

Chromedome45
December 10th, 2011, 03:24 PM
Thanks to all. Tried it out and it does work! Now I need an internal 800k floppy for it.

DFinnigan
January 12th, 2018, 11:40 AM
I do not believe it can support the larger EEPROM size that the Plus ROMs require,
Not true.


I want to say the 128k and 512k were a 64KB ROM, to the plus's 128KB ROM,
Correct.


and were never designed to read a 128KB rom, be it ROM or EEPROM.
Not true. The Mac 128K and 512K logic board supports 128KB of ROM; this is what made the 512Ke upgrade possible.



If memory serves, the the only difference between Mac 512k and 512ke was the ROM; the former had 64k ROM and the latter had 128K ROM, on identical logic boards.Correct, except that the 512Ke also had an 800K double-sided drive like the Macintosh Plus.