This application note discusses SIMCHECK version 2.12 which tests memory modules with parity-bit-disable logic chips.
INNOVENTIONS has recently received samples of memory modules with a strange chip device mounted on bit 9. Although the chips were marked with numbers like GS81C4100J70 or BP41C1000A-6, which are somewhat similar to the marking on real memory chips, our evaluation revealed that these chips are merely logic devices which disable the parity function. They do not have the memory function which is necessary for the real parity check available on true x9 (or x36) memory modules. These logic chips monitor the data read from the x8 (or x32) memory devices on the module and compute the correct parity bit for that data, regardless if the data was corrupted or not. Therefore, such modules disable the parity feature as defined by the IBM standard PC architecture.
When testing the module with parity-bit-disable logic chips on SIMCHECK, SIMCHECK will correctly identify the module as a x8 (or x32) since the parity-bit- disable logic chip has no memory.
Since SIMCHECK was designed to be a memory tester, it can test only memory devices. However, SIMCHECK program version 2.12 now supports the test of the x8 memory module with the parity-bit-disable logic chip when using the SIMCHECK SINGLE CAS ADAPTER p/n INN-8448-13.
To support this test, we have slightly modified the wiring of the SINGLE CAS ADAPTER in all units manufactured since May 12, 1994. To identify if your SINGLE CAS ADAPTER is already modified, there should be two 47K resistors on the area marked U2. If you have an older version of the SINGLE CAS ADAPTER, it can be modified, either at your end or by sending it to INNOVENTIONS (please call us for wiring change details).
Mount the SINGLE CAS ADAPTER onto the green SIP ZIF socket of SIMCHECK in accordance with Section 7.13 of the SIMCHECK manual. Install the module in the adapter's socket, and press F1 to test.
SIMCHECK will respond with the message:
BIT9: PARITY BIT
The test will then proceed with the normal SIMCHECK test in progress (TIP) animation with the letter 'p' placed at the position of bit 9. The final test result will show a message like:
0:08.4 ** ****** P
A "dummy" or a non-functioning parity-bit-disable chip will be noted on the display with '-', as in earlier versions of the SIMCHECK test program.
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