And of course there's always the lazier way of picking up a used 5004A or 5006A. They can be had for around USD$75.
Given that I already have a dump of the ROM, I should be able to lash up a simple Matlab script to process the file and derive the signatures - I think. And the SA0 signatures should just be the values from the bits of a binary count pattern (I think), which I can duplicate in Matlab, thereby validating my script.
But there is still the question about the difference(s) between the 5004 and 5006 - if you know.
And of course there's always the lazier way of picking up a used 5004A or 5006A. They can be had for around USD$75.
No no no, that would be cheating
If there is anyone else (besides Kjelt, who I've PM'd a couple of times) who has a broken 3468 and would like to follow or participate, please let me know.
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Maybe I should try a different chip, anyone a better candidate then the 2764A ( I have a batronix BX40 Bagero II programmer so can read everything in this list: http://www.batronix.com/pdf/BX40Bagero-II-DeviceList.pdf )
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You might want to try reading the MK3600 as an 87C64.
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Perhaps I should do the same as Sailor did, hook it up to a 8 bit microcontroller board and program my own readout sequence. Will take some time though.
You could also take a quick look at what's happening in the programmer with the data and address pins in relation to /CE transitions. And make sure power is showing up on the right pins.
But I don't think it's as simple as computing the CRC (that's really what the SA is doing) across all the bits in the ROM dump you have. Whereas SA0 disables the ROM, SA1 re-enables the ROM and holds processor pin 31 (P14) low.
My guess is that the processor samples P14 at boot and, if low, goes into a loop where it reads all the locations in ROM, and probably pokes at all the other places described in table 7-D-4.
I'm noticing on your little diagram in the upper right of your paper that the 2764 is numbered clockwise, which is incorrect when looking from the top. Maybe it's not wired right?
I'm noticing on your little diagram in the upper right of your paper that the 2764 is numbered clockwise, which is incorrect when looking from the top. Maybe it's not wired right?
Mark, Kjelt sent me a photo of his transition/adapter board - the ROM socket is on the underside of the board, so it's mirrored. Power, ground, and 27C64_20 --> ROM_20, etc all look OK.
I've had aquick look at JM503 while running SA1. It goes low for ~1msec, then high for ~20usec, then low again for more than 700msec before going high again to complete the cycle. I would like to think that the 1msec interval is the intended SA measurement window, but how is a 5004 to know? Or is the 'double window' just another symptom of what's wrong with my 3468A
Maybe the lower half contains a ROM check routine and if that's intact it can check the rest of the ROM and display an appropriate error. So, it's only critical that the lower half is ok.
Building an analyzer with an Arduino is going to take some really tight coding.
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I am sleeping 15 times (25MHz = 40ns) is 600ns which should be more then enough.
What do you guys think?
I am afraid that there is not enough room for a socket in the 3468a since the plastick powerswitch extension runs over it
So I would have to make some temporary thing then. That can easily be reversed.
I will have to see how to do that, any suggestions?
Its bedtime for now for me.
BTW, another open issue that we might discuss is with which other memory device we are going to replace the MK36000 if we have the final content. It could well be that we need a microcontroller to emulate it?