Tabajara A601 memory expansion

[Chartus]

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

Just a few questions.

1. Does it have to be FPM simms or can you use EDO simms instead ?
2. Can you use 30 pin simms instead?
3. Memory size doesn't matter?

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

[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!

[Chartus]

Thats good news.  I think I will give it a try.  Now to go dig out them old 1 meg 30 pin simms.

[rkauer]

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

 At least here in "Terram Brasilis"...

[Chartus]

Quick question.  Do I have to use 30 pin SIMMS in pairs.   What I'm asking is do I need 1 or 2 SIMMS.

[rkauer]

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

[Chartus]

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.

[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...

[Chartus]

That clears things up.  I will go with 2 1meg simms since I have some on hand.  Thanks for all the help.

[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:

[Chartus]

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 ?
 

[Chartus]

I have found an old 4 meg 72 pin simm (IBM)that I can use so I will probably go with that.  The fun part will be building it to fit in the trapdoor without taking the machine apart.

It will be a tight fit but I think I can do it.

[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.

[Chartus]

I haven't tried the 30 pin simms yet.  First I tried to get the 72 pin simm version to work.  Wired it up and the machine would boot but the memory count didn't change.  I looked at the russian papers and there is a difference in your A600 table and his.  I tried his but just kept getting yellow screens at boot.  I think I read that this was caused by chipmem problems.  I am not that great at soldering and right now I am sick trying to get this working.  Maybe I will try again later.  It might just be a bad stick of memory.

Hmmmm..... My first rant (I think)

[AeroMan]

When I've saw this name I was pretty sure this was posted by someone from Brasil...  :-D  :-D