A500 plus 2MB mod, what am I doing wrong?

avinitlarge · 15 June 2016, 19:52

Im trying to add a extra chips to a 512k board to bring it up to 2mb. I bought 8 new chips, fitted 4 and it shows the extra ram (512k), I piggy backed the other 4, Still 512k. Pin 17 the left 2 chips goes to Pin 11 of U32, Pin 17 the right 2 chips goes to Pin 5 of U32. I would have thought that this would have worked or have I missed something?

Zetr0 · 15 June 2016, 20:51

@avinitlarge

I like your style sir - you will need to ensure that the CE (Chip Enable) pin of top 512k bank is wired to the correct RAS line - do you have the schematics for the A500/A500+ if so it has all you need in there =)

Jope · 15 June 2016, 21:04

You're almost there. The crucial problem here is, that now both sets of RAM chips are still connected to the same memory bank.

There are CAS and RAS signals going to the DRAM chips.

In the original setup, the RAS signals are all shared among the chips and the two separate blocks of RAM have individual CAS signals.

In an A501+, we have two RAS signals and two CAS signals.

The A500's trapdoor connector has the RAS signals on pins 37 and 38. Check RAM chip's pin 4 on the expansion, and see whether they're connected to pin 37 or 38 on the trapdoor connector. Seems by the schematics that it should be pin 38 (XRAS1)

What you need to do is bend up pin 4 of the top chips and connect them all together, then connect that RAS bank to the unused RAS pin on the RAM expansion connector Should be pin 37 (XRAS0).

Double check the schematics for the A500 rev 6, A501 rev 6 and the A500+ rev 8 and A501+ to be sure.

Good luck!

Haha, this actually makes me want to make some ghetto A501+s too. :-)

avinitlarge · 15 June 2016, 21:57

Ha ah, Yes, just seen it on the schematic after you said, Silly me, I studied it for ages too.
Works now

Thank you
Just needs to be tidied up a little and the clock parts pulling out

Zetr0 · 15 June 2016, 23:34

Zetr0 is most pleased at this

spannernick · 16 June 2016, 01:43

Can you do this with any other Amiga..?

Jope · 16 June 2016, 06:23

Good show! This only works for the A500 plus.

demolition · 16 June 2016, 09:40

Or Rev. 8 A500s if you retrofit the missing logic to upgrade it to a full A500+ board.

ReadOnlyCat · 16 June 2016, 15:47

This setup definitely has a kinky feel to it.

You should probably shorten the long yellow wire though or tape it on the board so it does not float, it seems like it would be very easy to tear it apart by mistake along with a track or two.

The blue gunk on the top traces does tease my curiosity: w,as this due to a battery leak?

avinitlarge · 16 June 2016, 15:59

I've shortened the wire and tidied it all up. Took the clock components out and fitted them to another board.
The blue stuff is nail varnish, previous battery leak as you guessed ��

Amiga1992 · 16 June 2016, 18:30

Quote:

Originally Posted by Jope

Good show! This only works for the A500 plus.

I thought you could piggyback videocard RAM chips on an A600 for 2MB Chip, too.

Jope · 16 June 2016, 18:56

Quote:

Originally Posted by Akira

I thought you could piggyback videocard RAM chips on an A600 for 2MB Chip, too.

Sure, but those go on the motherboard. :-)

spannernick · 17 June 2016, 20:40

Can you do this on the A1200 to give it 4 meg..or is it just the A500 and A600..?

Sent from my GT-I9505 using Tapatalk

Amiga1992 · 17 June 2016, 20:42

Quote:

Originally Posted by spannernick

Can you do this on the A1200 to give it 4 meg..or is it just the A500 and A600..?

The modification you see is for Chip RAM. You cant't do that with Fast RAM.
And no you can't have 4MB of Chip RAM.

ReadOnlyCat · 18 June 2016, 08:39

Quote:

Originally Posted by Akira

The modification you see is for Chip RAM. You cant't do that with Fast RAM.
And no you can't have 4MB of Chip RAM.

Actually, with a very simple hardware extension consisting only of a few logic gates it would be relatively simple to implement bank swapping for Chip RAM. This way one could use way more than the original 2MB to store graphics and the likes (but one could not access it all at the same time, only 2MB of this memory would be visible at any moment).

Obviously, no existing software would be able to take advantage of it so that would be useful only for a modern developer but who knows? I definitely like the idea.

nogginthenog · 18 June 2016, 09:58

It's easier than that. Just move the chipram jumper into the 8MB position

15 June 2016, 19:52	#1
avinitlarge Registered User Join Date: May 2016 Location: Rotherham Posts: 65	A500 plus 2MB mod, what am I doing wrong? Im trying to add a extra chips to a 512k board to bring it up to 2mb. I bought 8 new chips, fitted 4 and it shows the extra ram (512k), I piggy backed the other 4, Still 512k. Pin 17 the left 2 chips goes to Pin 11 of U32, Pin 17 the right 2 chips goes to Pin 5 of U32. I would have thought that this would have worked or have I missed something?

15 June 2016, 21:04	#3
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	You're almost there. The crucial problem here is, that now both sets of RAM chips are still connected to the same memory bank. There are CAS and RAS signals going to the DRAM chips. In the original setup, the RAS signals are all shared among the chips and the two separate blocks of RAM have individual CAS signals. In an A501+, we have two RAS signals and two CAS signals. The A500's trapdoor connector has the RAS signals on pins 37 and 38. Check RAM chip's pin 4 on the expansion, and see whether they're connected to pin 37 or 38 on the trapdoor connector. Seems by the schematics that it should be pin 38 (XRAS1) What you need to do is bend up pin 4 of the top chips and connect them all together, then connect that RAS bank to the unused RAS pin on the RAM expansion connector Should be pin 37 (XRAS0). Double check the schematics for the A500 rev 6, A501 rev 6 and the A500+ rev 8 and A501+ to be sure. Good luck! Haha, this actually makes me want to make some ghetto A501+s too. :-) Last edited by Jope; 15 June 2016 at 21:13.

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15 June 2016, 20:51	#2
Zetr0 Ya' like it Retr0? Join Date: Jul 2005 Location: United Kingdom Age: 49 Posts: 9,768	@avinitlarge I like your style sir - you will need to ensure that the CE (Chip Enable) pin of top 512k bank is wired to the correct RAS line - do you have the schematics for the A500/A500+ if so it has all you need in there =)

15 June 2016, 21:57	#4
avinitlarge Registered User Join Date: May 2016 Location: Rotherham Posts: 65	Ha ah, Yes, just seen it on the schematic after you said, Silly me, I studied it for ages too. Works now Thank you Just needs to be tidied up a little and the clock parts pulling out

15 June 2016, 23:34	#5
Zetr0 Ya' like it Retr0? Join Date: Jul 2005 Location: United Kingdom Age: 49 Posts: 9,768	Zetr0 is most pleased at this

16 June 2016, 01:43	#6
spannernick Retro Nuts Join Date: Aug 2004 Location: London/UK Age: 53 Posts: 1,184	Can you do this with any other Amiga..?

16 June 2016, 06:23	#7
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	Good show! This only works for the A500 plus.

16 June 2016, 09:40	#8
demolition Unregistered User Join Date: Sep 2012 Location: Copenhagen / DK Age: 43 Posts: 4,190	Or Rev. 8 A500s if you retrofit the missing logic to upgrade it to a full A500+ board.

16 June 2016, 15:47	#9
ReadOnlyCat Code Kitten Join Date: Aug 2015 Location: Montreal/Canadia Age: 52 Posts: 1,178	This setup definitely has a kinky feel to it. You should probably shorten the long yellow wire though or tape it on the board so it does not float, it seems like it would be very easy to tear it apart by mistake along with a track or two. The blue gunk on the top traces does tease my curiosity: w,as this due to a battery leak?

16 June 2016, 15:59	#10
avinitlarge Registered User Join Date: May 2016 Location: Rotherham Posts: 65	I've shortened the wire and tidied it all up. Took the clock components out and fitted them to another board. The blue stuff is nail varnish, previous battery leak as you guessed ��

17 June 2016, 20:40	#13
spannernick Retro Nuts Join Date: Aug 2004 Location: London/UK Age: 53 Posts: 1,184	Can you do this on the A1200 to give it 4 meg..or is it just the A500 and A600..? Sent from my GT-I9505 using Tapatalk

18 June 2016, 09:58	#16
nogginthenog Amigan Join Date: Feb 2012 Location: London Posts: 1,311	It's easier than that. Just move the chipram jumper into the 8MB position

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