Replacing an MMU (344-0010-B)

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Replacing an MMU (344-0010-B)

I need to replace the MMU (part number 344-0010-B) on an Apple ][e.  Does anyone know of anywhere I can buy one?  Alternatively, does anyone know if it is possible to burn some kind of blank logic IC in order to reproduce an MMU?

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Is this the same part that

Is this the same part that gets replaced in a PAL IIe to change display line count and produce 50 Hz update? If so then it is a ROM and could in theory be replaced if you can read out the contents from a similar one. I guess the pinout might not be standard though. There is definitely info around about how it works and what each line does. I don't have it handy now but could search for it.

cheers, Nick

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344-0010-B

I found this site on the web: https://www.4starelectronics.com/part_detail/3440010B.html

 

I found others sites as well, but they all link back to the same company. To me, that technique is related to scams.

 

For some reason, every site was you to request a quote.

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This schematic shows how the

This schematic shows how the MMU is connected:

https://downloads.reactivemicro.com/Apple%20II%20Items/Hardware/IIe/Schematic/Apple%20IIe%20Schematic%20-%201.jpg

It seems to be acting as a DRAM controller, it basically buffers the address bus from the 6502 onto the DRAMs and performs some decoding logic. Unfortunately the decoding is pretty complicated because of the different modes and so on that the machine can be in. There are some other schematics in the same directory which seem to show the internal logic (I think may be leaked schematic of Apple IIe prototype hardware). So it's not easy to make one's own -- probably possible using a CPLD, but would be a months long project so not something I would tackle, and also the result would be a bit ungainly since it would sit above the PCB in an adapter PCB to get it into the 40 pin pinout.

The best option is to buy one. Surely it must be possible to buy an Apple IIe motherboard from a failed machine to use for parts?

cheers, Nick

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MMU stands for Memory

MMU stands for Memory Management Unit.

It actually combines and replaces a bunch of TTL logic chips. The MMU internals are covered into the Understanding the Apple IIe book by Jim Sather (see chapter 5).

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I have one spare from a parts

I have one spare from a parts mainboard. 

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Thanks Timelord, I've sent

Thanks Timelord, I've sent you a DM

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Thanks amauget, I didn't know

Thanks amauget, I didn't know the MMU was covered in that book.  As apple basically introduced the MMU as a way of stopping other companies cloning their hardware, I guessed that finding any documentation on it was probably unlikely.  I'd considered trying to work out what might be in the MMU by comparing a IIe schematic and a II or II+ schematic, but that is a last resort.  I may look at recreating the MMU using the information in Understanding the Apple IIe though.  For now I'm hoping I can get an original IC, but I will probably still try and come up with an alternative as they are only going to become rarer and it would hopefully be useful for others.

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