Tabajara A601 memory expansion

[rkauer]

Chartus wrote:
I think I will try this hack since I can't find a real A601 trapdoor expansion in the US.

Just a few questions.

 As the "father" of it, I think I can tell you.;-)

1. Does it have to be FPM simms or can you use EDO simms instead ?

 Nope, EDO chips don't work. Dunno why, but it is something related to RAS/CAS timing.:headwall:

2. Can you use 30 pin simms instead?

 Yes! But you need to re-make the wiring to match the 30-pin SIMM pinout. And doing the hack with 30pin you'll get a "bonus": don't need to open the case to slot-in the expansion.
 
 Another small "bonus" is you'll only find FPM SIMMs!

3. Memory size doesn't matter?

 You need only to use SIMM of 1, 4 or 8Mb. Less is obviously a waste of time, more and you hit in other issues due the way SIMM bank pins are distributed. Believe me, I investigate the area a lot before write the hack.

If these are stupid questions feel free to laugh  ;-)

 :lol:  ..... erm... don't!!!!

 Your questions are not stupid, they are valid points to the hack. Cheers, mate!

[rkauer]

 You can use 4Mb 30pin SIMM too! Only issue is they are very hard to find...

 At least here in "Terram Brasilis"...

[rkauer]

 Just one, of course. It only must be 1 or 4Mb.

[rkauer]

Chartus wrote:
Just one?  Looking at the 30 pin SIMM pinout it looks like there are only 8 data pins.  Dont I need 16 data pins?  Or do I just connect the first 8.

 Oops! Forgot about it! :oops:

 Yes, you need a pair of 1Mb 30pin. Or just one 4Mb (routing the additional data to the "other" bank). Two banks will be lost (no way to utilize 'em). Note that in this case you need a major rework (using a multiplexer circuit to achieve the necessary signals). Two SIMM are a more viable way.

 If you want to know a bit more, read this PDF...

[rkauer]

 Some days my brain don't help me.

 Yesterday was one of those days!

 You need only one 30 pin SIMM!!!

 Data bits are always 8bits, nothing more!

 Damn me! Bad brain! Bad, bad brain! :crazy:

[rkauer]

Chartus wrote:
So just wire up the first 8 data lines?  I notice that the a600 trapdoor has 16 data lines.  Do I just leave the unused address lines N/C ?

 If the SIMM have the address lines (8Mb - rare as hen's teeth), short them to ground. Never leave an address nor any other input signal floating (not connected).

 My prototype use the 16bits data lines (because they are there), but I'm think this is not necessary.

 Tell me if it works, the worst case scenario is the hack will not work or cause a guru on boot. It will not burn your Amiga. Just be careful with the wiring and that's all.

[rkauer]

 A600's trapdoor pin67 is 14.3MHz from the motherboard. Not connected in the SIMM. It uses the RAS/CAS signals as clock.

 Pin #75 is not connected to anything! It have a 470 Ohms resistor internally on the A600 board!

 I simply put the description of the pin assigns on bellow the document for people willing to make his/hers/theirs own hacks!

 Remove the resistor, leaving the pin floating. Then try again.

 If still not working, use A600's CASx(0) instead of CASx(1). Explaining a bit better:

 Use pin 43 instead 46 : CASU(0) instead CASU(1)
 Use pin 45 instead 44 : CASL(0) instead CASL(1)

 Oh, BTW: I think Aeroman was talking about me. You didn't notice my accent?

 :-)

[rkauer]

 Then some more hints. If don't work, drop it, your A600 motherboard revision may not work with the hack.

 BTW: what revision it is? 1.0 (A300)? 1.3 (buggy)? 1.5? 2B or 2D?

 Green screen means "almost good", the Amiga found the memory but wasn't able to configure it. Check the traces/wires, specially the address ones. And be sure to use a working SIMM, too.

 What speed is your SIMM? It must be 70~80ns (like the RAM chips on the A601 itself). Faster SIMM are no good, since they could not hold the information for enough time (too slow refresh rate from the Amiga).

[rkauer]

 You need the caps on the +5V rail! Without it the voltage ripple will cause bad behaviour (from the Amiga, you don't wanna attack grandmas).

 One 47uFx10V will suffice. Install it in the middle-most +5V contact. Measure the voltage level before and after the modification.

 If the PCI slot is too loose, it could be the cause of no-working hack. Try to tight it a bit using a small "hook" shaped tool.

[rkauer]

 Congratulations!

 Is good to hear about someone who was able to do my hack!

 For filling the HD, I suggest you start from here.

 Classic Workbench for A600 (ECS) is very good and you will not regret it!

 You need to tweak it a little after the set-up, and need a 50Mb or more boot partition, but it is a superb start.

[rkauer]

Protek wrote:
I'm keen on trying this memory upgrade myself, since I'm packed with 72 pin SIMMs dunno, whether they're EDO or FPM, though. Would it be possible to design and fabricate a PCB for this? I guess the available space is the limitation?

 Yeah, the space for the hack is tight. Better stick with the "wired" version. Just keep the wires short enough and only use FPM SIMM. 70~80ns are the best for it.

 If you don't know if the chip is FPM or EDO, look directly on chip and Google for "code-of-the-chip datasheet alldatasheet".

 The http://alldatasheet.com is simply the best site for information on semiconductors!