| Memory Presence Detection |
WARNING
If you use a Multimeter to check the connections on the Presence Detection Pins: Do not touch other pins than these 5 shown below !
The memory module might get damaged from the testing voltage of your Multimeter.
Also obey the usual rules for antistatic device handling !
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Most newer IBM PS/2 machines use the 72-pin Single Inline Memory Modules (SIMM) on either planar or memory expansion cards.
Very often there are more than one of these 72-pin connectors available and one might wish to upgrade the memory with adding another memory module.
But: the machine comes up with a nice 215-error code and the error-code list says it were "Check memory, it might be wrong type or wrong speed".
"How can the system know that ?"
Pretty simple: There are 4 pins reserved on the module, which are called 'Presence Detect Pins' - and which tell the systemboard
- if there is a module installed
- which is the size of the module
- which access-speed it is
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Memory Presence Detection Pins
ECC/PAR (Pin 48)-------------------------- -+
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PD Bit0 (Pin 67)------------------+ |
PD Bit1 (Pin 68)----------------+ | |
PD Bit2 (Pin 69)--------------+ | | |
PD Bit3 (Pin 70)------------+ | | | |
GND (Pin 72)--------+ | | | | |
| | | | | |
V V V V V V
+------------------------- --- ---------+
| # # # # # # # # #.. # .. # # # |
| # # # # # # # # # # # # # |
| |
| 7 7 7 6 6 6 6 6 6 4 0 0 0 +-+
| 2 1 0 9 8 7 6 5 4 8 3 2 1 |
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Pinout Table
Valid for IBM PARITY-Modules
Pin 48 = Not Connected
Pin
70 | Pin
69 | Pin
68 | Pin
67 | Size | Speed | Notes |
| o | o | o | o | | | Free or Invalid |
| o | o | o | X | 1 MB | 120 nS | |
| o | o | X | o | 2 MB | 120 nS | |
| o | o | X | X | 2 MB | 70 nS | |
| o | X | o | o | 8 MB | 70 nS | |
| o | X | o | X | 16 MB | 70 nS | |
| o | X | X | o | 2 MB
32 MB | 80 nS
70 ns | On older machines
IBM P/N 92F7205 or 92G7206 |
| o | X | X | X | 8 MB | 80 nS | |
| X | o | o | o | | | Reserved (*1) |
| X | o | o | X | 1 MB | 85 nS | |
| X | o | X | o | 2 MB | 85 nS | |
| X | o | X | X | 4 MB | 70 nS | |
| X | X | o | o | | | Reserved (*2) |
| X | X | o | X | 1 MB | 100 nS | Note (*3) |
| X | X | X | o | 2 MB | 100 nS | |
| X | X | X | X | 4 MB | 80 nS | Note (*4) |
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o = Not connected to GND (Pin 72)
X = Connected to GND (Pin 72)
All Modules are Parity ! |
- This is an accepted coding for the 8MB-module used in the N51SX - see Jim Shorney's Modification on the Selfmade Memory Page for details.
- This is an accepted coding for the 4MB/80nS-module P/N 79F3988 / 79F1000 (FRU 79F1003) used on the L40SX (8543), see the Selfmade Memory Page as well.
- This is an accepted coding for the 8MB/80nS-module P/N 79F3989 (FRU 79F1004) used on the L40SX (8543), see the Selfmade Memory Page as well. However: It must be a single-sided module with chips that have the typecode -LJP8 after the sizecode !
- This is an accepted coding for the 2MB/80nS-module P/N 79F3987 (FRU 79F1002) used on the L40SX (8543), see the Selfmade Memory Page as well.
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Pinout Table
Valid for ECC and NON-PARITY-Modules
ECC modules have Pin 48 tied to Pin 72 = GND
Pin
70 | Pin
69 | Pin
68 | Pin
67 | Size | Speed | Notes |
| o | o | o | o | | | Free or Invalid |
| o | o | o | X | 16 MB | 60 nS | Non-Parity |
| o | o | X | o | 32 MB | 60 nS | Non-Parity |
| o | o | X | X | 4 MB | 60 nS | Non-Parity |
| o | X | o | o | 8 MB
8MB | 70 nS
70 nS | Non-Parity
IBM ECC FRU 92F0098 |
| o | X | o | X | 1 MB
16 MB
16MB | 70 nS
70 nS
70 nS | Non-Parity
Non-Parity
IBM ECC FRU 96F9100 |
| o | X | X | o | 2 MB
32 MB | 70 nS
70 nS | Non-Parity |
| o | X | X | X | 4 MB | 70 nS | Non-Parity |
| X | o | o | o | 8 MB | 80 nS | Non-Parity |
| X | o | o | X | 1 MB
16 MB | 80 nS
80 nS | Non-Parity |
| X | o | X | o | 2 MB
32 MB | 80 nS
80 nS | Non-Parity |
| X | o | X | X | 4 MB
4MB | 80 nS
70 nS | Non-Parity
IBM ECC FRU 92F0097 |
| X | X | o | o | 16 MB | 70 nS | IBM ECC |
| X | X | o | X | | | |
| X | X | X | o | | | |
| X | X | X | X | 8 MB | 60 nS | Non-Parity |
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o = Not connected to GND (Pin 72)
X = Connected to GND (Pin 72) |
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