Piggyback RAM - TMM41464AP??

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Por sd_snatcher

Prophet (3471)

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20-09-2012, 01:56

Connect the A16,A17 and A18 of the RAM to the pins MA16, MA17 and MA18 of the S1985.

You should get the S1985 datasheet here.

Por RetroTechie

Paragon (1563)

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20-09-2012, 04:27

Ah good so the SRAM hookup for /CE etc at least works enough to boot the machine - getting there. Smile

Colemu wrote:

Update: boots but nothing loads. Obviously adjustments required. If you can advise RT, it would be appreciated. Cool

That's because ROM address lines 14 & 15 aren't MA14 / MA15 (or even Z80 A14/A15). So 16K blocks from the SRAM are addressed in a weird manner (I don't feel like checking, but you've probably got a 16 or 32K RAM machine now).

You need to use MA14 / MA15 from the S1985. Schematic says they're not used anywhere, so there's no way to get around soldering to the S1985 directly - be careful! (I pull wires from an 80-wire IDE cable for jobs like this). Also MA16 / MA17 and MA18, it'll get crowded in a spot there. Wink

Btw. HB-F1XD schematic also shows MA14-MA16 that go from IC15 (MB64H444) to ROM. Forget those - you need the same-named signals from S1985 only.

512K may not work right away, this is because MA18 doubles as a keyboard signal (KBDIR). Not used in this machine, but it might be set to that function on reset (see beginning of "3. Selection of functions" for details).

Por Colemu

Hero (535)

Imagen del Colemu

20-09-2012, 09:37

Thanks for that datasheet sd, very handy Big smile

Are pins MA16, 17, 18 used anywhere RT so that I don't need to solder directly? Question

I don't trust myself with too much soldering in such a small area Tongue

Por Colemu

Hero (535)

Imagen del Colemu

20-09-2012, 23:33

Now soldered, says 256kb RAM at bootup Question

Update: testram says slot 3.3 064k size

syntax error in 220

Bootup still says 256k.

Games load but corrupt screens

Por RetroTechie

Paragon (1563)

Imagen del RetroTechie

20-09-2012, 23:46

You have MA16/17/18 wired up now? If so, and a (decent) mapper test detects it as 64K, then you've probably got a short circuit somewhere between the higher address lines. Chances are somewhere on those S1985 pins.

Check your work with a magnifying glass, and (with power off) measure continuity between individual MA14-18 signals. Or like I said, do in individual steps 64 -> 128 -> 256 -> 512K and make sure all mapper tests pass before taking next step. Btw: does it test 100% okay as a 64K mapper?

Por Colemu

Hero (535)

Imagen del Colemu

20-09-2012, 23:59

I have 14, 15, 16, 17 & 18 all wired to the S1985. Tested all connections with a multimeter and all ok. No contact with corresponding pins as I checked that with the multimeter too.

The testram program gives a error (see above) syntax error in 220. Used to work ok with the previous ram.
Is it to do with the MA18 being shared with another signal?

Additional - I got the 5v from the ROM bellow, should I have got it elsewhere?

Por RetroTechie

Paragon (1563)

Imagen del RetroTechie

21-09-2012, 00:05

Colemu wrote:

Is it to do with the MA18 being shared with another signal?

Very possible, can you disconnect MA18 temporarily, connect that SRAM pin to GND or +5V (doesn't matter which), and run tests again?

Quote:

Additional - I got the 5v from the ROM bellow, should I have got it elsewhere?

No, isn't too critical so should be fine (short / thick wire is good for supplies, and an IC pin qualifies as such).

Por Colemu

Hero (535)

Imagen del Colemu

21-09-2012, 00:21

Runs, and tests 64k at 3.3 ram fine

Also ran test on memory mapper at 3.3 - all tests fine (256kb)

Por msxholder

Champion (382)

Imagen del msxholder

21-09-2012, 00:32

ma 18 is also controlled for an keyboard dir signal .
You have to set it's function before reset !

Por Colemu

Hero (535)

Imagen del Colemu

21-09-2012, 00:37

way over my head oO

How do I do this? Question Is there a way I can set it to default to MA18 function and not Key/DIR?

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