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SIMMS_ SIMM Module Pinout
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SIMMS.txt
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2014-09-28
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Industry Standard SIMM Modules:
PIN No. PIN NAME PIN No. PIN NAME PIN No. PIN NAME
1 Vcc 11 A4 21 WE-L
2 CAS-L 12 A5 22 Vss
3 Data Bit 1 13 Data Bit 4 23 Data Bit 7
4 A0 14 A6 24 NC
5 A1 15 A7 25 Data Bit 8
6 Data Bit 2 16 Data Bit 5 26 Q9
7 A2 17 A8 27 RAS-L
8 A3 18 A9 * 28 CAS9-L
9 Vss 19 NC 29 D9
10 Data Bit 3 20 Data Bit 6 30 Vcc
* pin 18 is A9 for 1M SIMMs and NC for 256K SIMMs
IBM PS2 Model 30/286 - System Board RAM Module Connector Pin Assignments
Pin I/O Signal Pin I/O Signal
1 N/A +5V (Vcc) 2 I -Column Address Strobe
3 I/O Data Bit 1 4 I A0
5 I A1 6 I/O Data Bit 2
7 I A2 8 I A3
9 N/A Ground (Vss) 10 I/O Data Bit 3
11 I A4 12 I A5
13 I/O Data Bit 4 14 I A6
15 I A7 16 I/O Data Bit 5
17 I A8 18 I A9
19 N/A No Connection 20 I/O Data Bit 6
21 I -Write Strobe 22 N/A Ground (Vss)
23 I/O Data Bit 7 24 0 Presence Detect 1 = Gnd
25 I/O Data Bit 8 26 0 Presence Detect 2 = Gnd or Open *
27 I -Row Address Strobe 28 N/A No Connection
29 I/O Data Bit 9 (Parity) 30 N/A + 5V (Vcc)
* Note: Pin 26 is Gnd if a 1Mx9 memory module is installed and Open
if a 256Kx9 memory module is installed.
(Since the model 30/286 can't use 4 megabyte SIMMs, they aren't considered here.)
Conversion Steps:
To make standard 1M SIMMs work in an IBM, the following conversions
must be made:
1. Ground Pin 24
2. Disconnect Pin 26 from Q9
3. Ground Pin 26
4. Connect Q9 to pin 29
5. Disconnect Pin 28 from CAS9
6. Connect CAS9 signal to pin 2
If this sounds like it would be hard to do on a small, surface
mounted SIMM module, you're right! Fortunately, the SIMMs I've
looked at have little jumper pads on the back that can be cut with
an Xacto knife and bridged with a soldering iron. The pads are
located in the circuit in exactly the right configuration to make
these changes. If your SIMMs have the jumpers, and you are
comfortable with performing those modifications, then you're in
luck. It will take about five minutes per SIMM. Otherwise, you'll
have to pay a premium price for "IBM" SIMMs.
Final Note: The layout of the jumper pads on the SIMMs allows for
the grounding of pin 28. Perhaps it is used for a presence detect
for 4M SIMMs in IBM machines that can accept them.