1MB CHIP RAM replacement board for A500+

[Kai]

Just done a total respin of this, based around newer 40-pin SOJ ISSI DRAM chips - IS41C16257-35's and using SMD 1206 capacitors

This will give a total of 1MB (8Mbit) of CHIP RAM and shouldn't impinge on anything in the trapdoor slot - literally a 1:1 replacement of all the 256k x 4 DRAM chips. Gerbers are all updated as well.

Again - GPL v2 on all of my projects, to fork them, play with them, whatever you'd like. Remember to grab A500 Parts symbols, which have been updated, too.

https://github.com/kr239/A500-DRAM-Board

[Kai]

Added this to PCBWay for people wanting to just order PCB's quickly:

https://www.pcbway.com/project/share...ent_Board.html

[jediknight]

awesome but how do i install it?

[Kai]

Originally Posted by jediknight

awesome but how do i install it?

Step 1) Get PCB
Step 2) Install components
Step 3) Remove the IC's from their sockets
Step 4) Plug this in to the IC socket space

I'm assuming you'll have removed the IC's, or will have soldered IC sockets in place, as there's no reason for you to use this board, unless you have faulty RAM and you don't want to go trawling through eBay for chips from dodgy chinese sellers.

It was originally designed for the soon-to-be-released A500++ boards.

[Mick]

Originally Posted by Kai

It was originally designed for the soon-to-be-released A500++ boards.

The what now?

[talybont]

Originally Posted by Kai

Step 1) Get PCB
Step 2) Install components
Step 3) Remove the IC's from their sockets
Step 4) Plug this in to the IC socket space

I'm assuming you'll have removed the IC's, or will have soldered IC sockets in place, as there's no reason for you to use this board, unless you have faulty RAM and you don't want to go trawling through eBay for chips from dodgy chinese sellers.

It was originally designed for the soon-to-be-released A500++ boards.

I'm also struggling with how this connects to the motherboard. In the BOM it says "16 x 10-pin SIL Headers (Harwin M20-9771042)", but where on this board do you solder that many pin headers? I can't find the holes for them. Or are this to be soldered on the motherboard?

[Monkey]

Originally Posted by Kai

don't want to go trawling through eBay for chips from dodgy chinese sellers.

Just been through this very exercise... only had 1 bad chip out of 25... luckily I only needed 16 chips! All tested and working fine.... did take 2 hours to run through all 99 tests though.. and I still have 8 good chips as spares.

[hooverphonique]

Originally Posted by talybont

I'm also struggling with how this connects to the motherboard. In the BOM it says "16 x 10-pin SIL Headers (Harwin M20-9771042)", but where on this board do you solder that many pin headers? I can't find the holes for them. Or are this to be soldered on the motherboard?

That info is clearly wrong.. The address lines are the same for all ram chips, so they are taken from one of them. Each chip then has 4 data lines which have to be brought in, and left over is just a few ras/cas signals. This board is thus for an Amiga with 4 OE ram chips, and not 16.

[Kai]

It's for an A500+ - with both RAS0 and RAS1 lines. You're correct - all RAM chips have A0 to A8 being fed in but as the originals are 4 bits wide, you need 4 to deal with D0 to D15 - plus there's the upper CAS and lower CAS to consider, too.

The info is not 'wrong' either - you just don't need to add loads of redundant pins to the board - as long as you have:

A0 to A8
D0 to D15
GND
VCC
UCAS
LCAS
RAS0
RAS1
WE

then you're good to go. There are a few redundant GND and VCC pins just because i felt that a single GND and VCC wasn't enough.

[hooverphonique]

Originally Posted by Kai

The info is not 'wrong' either

Let's agree to call it misleading then, if the BOM specifies 16x10 header pins

[Kai]

16 strips of 10 then, however you want to phrase it.

[robinsonb5]

Originally Posted by Kai

16 strips of 10 then, however you want to phrase it.

But why 16 strips? I count 38 through holes on the picture in your first post - surely 4 strips would be sufficient? Or am I missing something obvious?

[jediknight]

werent that a500++ board coming out in 2011?

[Kai]

Originally Posted by robinsonb5

But why 16 strips? I count 38 through holes on the picture in your first post - surely 4 strips would be sufficient? Or am I missing something obvious?

...you know what - you're absolutely right! XD

I was looking at the BOM and the mouser cart for the rev1, which did use all the original DIP socket pads - so apologies for getting that wrong, i'll update that later today

[Kai]

Originally Posted by jediknight

werent that a500++ board coming out in 2011?

a1k.org released an A500+ board, but once they sold them all, and ran out of parts to sell with them, they stopped the run.

The new A500++ has been reverse engineered by Rob Taylor and looks like this:



This will be available soon.

[project23]

Oooooooh sh^tballs... you mean to say this will be open?

[Mick]

Very nice!

[Kai]

Originally Posted by project23

Oooooooh sh^tballs... you mean to say this will be open?

Not initially - but they won't be expensive

[Mick]

When that's done has he considered doing a spinoff that supports 8372A Agnus? 2MB Agnus's are getting a bit hard to come by now. He could call it the Amiga 500+-

[Kai]

Haha - this is mostly for the resurrection of A500+'s that have been killed off by VARTAAAAA