Plus ROMs on a 512ke board

[RickNel]

Excuse the simple question.. I want to play safe.

I have a working Plus logic board, and I have a 512ke that fails ROM read. Replacing electro caps with tants didn't solve it.

Is it really safe to swap the Plus ROMs into the 512ke logic board to test?

Even better, can I duplicate the Plus ROMs (if they work) to EPROMs for the 512ke?

I have a couple of ROM programmers. If burning ROMS for a Compact Mac, should I use JDEC, hex, or binary format for the files?

Rick

 

[mcdermd]

No problem at all. Apple did this themselves and called the resulting product a Macintosh 512ke.

 

[onlyonemac]

If you find that it is indeed the ROMs that are at fault, then try making an EPROM copy of the Plus ROMs and use those permenantly for the 512ke. I cannot give advice as to how to copy the ROMs, but ask dougg3, as he has had loads of experiance using EPROMs in Macs.

 

[RickNel]

Just to round this off - I finally got some 27C512 EPROMs through the mail. It only took a few seconds to copy the Plus ROMs, burn and verify. They are 100ns EPROMS and seem to boot the 512k logic board even a little faster than the original Plus ROMs. And I have backup files, which is a nice feeling.

 

[Gorgonops]

If the EPROMS boot the machine any faster than the original ROMS it's not because they're 100ns parts. There's no magical speed auto-sensing going on with any memory parts in machines that old; they're either fast enough to do the job or they're not.

There were several *versions* of the Plus ROM, perhaps the disk driver was slightly faster in some vs. others.

 

[CC_333]

Hi

I'm not totally sure, but I think he meant to say that the copies he made (in the form of the EPROMS) are slightly faster than otherwise identical originals (the original Plus ROMs he used as a basis).

c

 

[uniserver]

It might just be a perception thing, It's like when you get a new full set of tires on your car, Rides like a new ride or when get the noisy exhaust finally fixed. Sounds like a new car, and some how seems to accelerate much faster wow! What it really is because your exhaust was loud before you never gunned it too much because it would get louder

I swore the socketed SE/30 was faster then the soldered one, come to find out after I did specific bench testing, It was all in the hard drive's, one happened to be much faster, (the one installed in the Socketed SE/30)

 

[RickNel]

Yes - it is a perception thing. I don't have software to do meaningful tests on the 512ke, which is a single-floppy setup. I suppose I could more easily test the EPROMs on my Plus logic board with SCSI HDDs and ZIP. Maybe it's just a momentary joy that will fade with the next problem :-/

Rick

 

[Gorgonops]

Just for grins I looked up the datasheet for the 27C512 to make sure and yeah, it doesn't have any "data good" signal or anything else that would allow a computer to "clock faster" with, say, a 100ns part vs. a 150ns one. It has a "Chip Enable" signal which tells the chip to "wake up" and look at its address lines for the location of the byte you're requesting, and an "Output Enable" which tells it to actually shove the byte out its data lines. (It has this so a computer designer can dispense with the need to have a protective buffer in front of the device to keep it from fouling the bus while it's "thinking".) If the computer it's plugged into brings up OE too quickly and tries to use a value read from it before the output has stabilized then the value is likely to be garbage, and the part has no way to tell the host it's doing it. So, yeah. No matter how fast a part you stick in there it's going to run at the speed of the original unless you make changes to the circuitry of the computer to reduce the delay/increase the clock speed/whatever.

Anyway. If it was broken before and works now it runs infinitely faster. So you're still right!