Piggyback RAM - TMM41464AP??

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Por RetroTechie

Paragon (1563)

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22-09-2012, 22:41

Strange... IC13 combines /SLT33 with Z80 /BUSACK signal, and I don't know why (normally /BUSREQ and -ACK aren't used in an MSX). Question Seems to have something to do with that speed control IC, maybe it's interfering with normal /SLT33 function. Thoughts:

  • Maybe the DRAM's /CAS (not the generic /CAS from S1985 btw!) is really as good as /SLT33 in this case. Luck really is on your side, dude!
  • Maybe signal on pin 3/4 of IC13 is what's needed here (as opposed to /SLT33 signal on pin 2).

Por Colemu

Hero (535)

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22-09-2012, 22:41

Yeh, pin 2 of IC13 doesn't work. Does the above mean try pin 3 or 4 of IC13 or 3 & 4 combined? Question

Por RetroTechie

Paragon (1563)

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22-09-2012, 22:59

Schematic says pin 3 & 4 are connected so that's the same signal ("/SLT33 and not /BUSACK"). I suppose that speed control IC takes control of the Z80 bus from time to time, /SLT33 may get activated during such a period, and this shouldn't happen (hence IC13 keeping pin 3/4 signal high when /BUSACK is active).

Por Colemu

Hero (535)

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22-09-2012, 23:15

Nope doesn't work either mate
2 and 3/4 boot but nothing loads.....

Direct to S1985 doesn't pass TestRAM (PIN 56 is SLT33)

Should I map to different location do you think?

Update: just sent you the S1985 Manual I'm using. Maybe you can see if I was using the right PIN

Por RetroTechie

Paragon (1563)

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22-09-2012, 23:25

I have S1985 datasheet thx (since, ehm.. 20 years or so)

If nothing else works, I guess it's /CE back to the DRAM's /CAS (=IC13 pin 6) like you had before. Can't figure out why /SLT33 (or IC13 pin 3/4) wouldn't work though. Evil

Por Colemu

Hero (535)

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22-09-2012, 23:26

OK mate, will do. Hope it still works Tongue

Por Colemu

Hero (535)

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22-09-2012, 23:46

Connected to pin 6 on IC13.

now fails second pass page 7

Second time fails second pass page 20 & 23

Seems to slow down and speed up at times on the second pass.

Used to be same speed all the way through and passed every time Question

Por RetroTechie

Paragon (1563)

Imagen del RetroTechie

22-09-2012, 23:53

Only difference the schematic shows, is a ferrite bead (FB2) in between. So pick up in same point as before (IC16/17 pin 16).

If that works as before, perhaps best method would be to pick up that IC13 pin 3/4 signal through a series resistor (47 to 100 Ohm or so). Yeah sometimes it's tiny things like this that make difference between fail/succeed. Hannibal

Por Colemu

Hero (535)

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23-09-2012, 00:34

Bl**dy hell, still failing TestRAM Evil

Update: failed 1st 2 x tests. Just turned off, and tried again, now passed, strange

Nope, failed again. Just the odd page, every now and again, on the second pass

Por RetroTechie

Paragon (1563)

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23-09-2012, 02:00

I don't get it. Everything connected the same again as what worked okay before, and now it doesn't? Question

Check your work: no short circuits anywhere? Damaged pcb traces? Some other wire came loose? Compare current connections with pictures you posted.

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