Blizzard 1220 RAM project

[coze]

I've been tinkering with my 1220 last night to figure out how the RAM is organised. Maybe some of you know, this board has 4 mb onboard, and an optional RAM board exists to make it to up 8 mbs. To my relief it's not very complicated, I think I figured out how to install the second 4 mb.

Here's what I've found out for parties interested :

the RAM is organised as 8 1mx4 chips. here's the pinout of chips.



organisation of RAM chips :

CHIP # 1 3 5 7
CHIP # 2 4 6 8

connector

pinout of the optional RAM connector :

1 ............................. 30
60 .............................. 31

signals :

1 - VSS
2 - IO
3 - IO
4 - IO
5 - IO
6 - Chip 1&2 CAS
7 - OE & VSS
8 - IO
9 - IO
10 - IO
11 - IO
12 - OE & VSS
13 - IO
14 - IO
15 - IO
16 - IO
17 - CHIP 5&6 CAS
18 - OE & VSS
19 - IO
20 - IO
21 - IO
22 - IO
23 - OE & VSS
24 - A9
25 - A7
26 - A5
27 - A3
28 - A1
29 - VSS & OE
30 - Mystery pin #1
31 - WE
32 - Mystery pin # 2
33 - A0
34 - A2
35 - A4
36 - A6
37 - A8
38 - VCC
39 - CHIP 7&8 CAS
40 - IO
41 - IO
42 - IO
43 - IO
44 - VCC
45 - IO
46 - IO
47 - IO
48 - IO
49 - VCC
50 - CHIP 3&4 CAS
51 - IO
52 - IO
53 - IO
54 - IO
55 - VCC
56 - IO
57 - IO
58 - IO
59 - IO
60 - VCC

All chips share the same RAS which is not present on the RAM connector.
This RAS is tied to a pin on one of the GALs. Curiously the next pin on the GAL is connected to Mystery pin #1. So I take this is the RAS line for the expansion RAM.

Mystery pin #2 is a little bit more complicated. It's tied to GND via 472 smd resistor. When checking the pics at AHD it seems it's connected to the jumper block on the RAM expansion board.

http://amiga.resource.cx/photos/phot...res=hi&lang=en
http://amiga.resource.cx/photos/phot...res=hi&lang=en

so I was thinking this is some kind of enable pin for expansion RAM. if it's low the memory controller don't check for expansion RAM, but it's high (probably shorted to VCC on the exansion board via jumper) memory controller checks for expansion RAM.

I would like to have some opinions though before I see the magic smoke rising from my 1220 I'm thinking of piggy backing some soj 1mx4's I desoldered from some EDO SIMMs. connect RAS lines to the mystery pin #1, and short mystery pin #2 to VCC.

any thoughts ?

[DJBase]

I did an 4 MB Addon Board already. There will be a production run soon. So if you want such a board just let me know.

[Zetr0]

@Coze

looking at those pinouts I do belive that you could piggy-back the RAM chips and just tie-up a new RAS to the legs of them to the expansion port.

you would need to change the jumper on the board for 8mb though =D


@DJBase

interesting, have you got some pics of your adapter? and sources you would like to share?

[DJBase]

All I can show by now is the layout...

[Zetr0]

Looks like you spent a bit of time on that,

I have to admit I do enjoy seeing your work, very professional =D

[DJBase]

I like it professional so I always do my best

[coze]

yup it looks great I think I'll wait for DJ's board before piggybacking my stuff. If the price is right it won't be worth the trouble ... Also another reason is I can't trust my RAM to be working as I used a lighter on SIMMs to desolder them it would be a nightmare to find if one of them is faulty ...

having said that, does anyone know a good cheap kit to check RAM chip functionality ?

[Paul_s]

Originally Posted by DJBase

I like it professional so I always do my best

very pretty, now in water colours please!

[Secret Vampire]

Originally Posted by coze

having said that, does anyone know a good cheap kit to check RAM chip functionality ?

If you could find an old RAM tester which takes DIP chips you could build or buy an adaptor for SOJ chips with a zif test socket on it.

alternatively you might be able to attach a test socket in place of one of the chips on a known good simm and use an old 486 motherboard with memtest86 as a test rig.