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PS/1 - Adapter timing incompatibility
Applicable to: World-Wide
Service Information:
Some adapters which generate fast interrupts may not operate correctly on some PS/1 '486 systems. The IBM 16/4 Token Ring Adapter is one example and others are likely.
The cause is a chip from VLSI Technologies called the 82C002. The 82C002 is an ISA interface chip. Unfortunately, it requires ISA adapters to provide interrupt request pulses at least 300ns long. The interrupt request pulse generated by the 16/4 Adapter II is typically only 216ns long. Several other adapters also generate interrupt requests less than 300ns long. The ISA spec says that these interrupt request pulses can be anywhere in the range from 125ns to 1000ns. The fix was to add another VLSI Technologies module called the 82C480 to the motherboard. This lets the system work with pulses as short 125ns, thus providing downward compatibility with existing adapters (that are otherwise in spec).
The chip(s) can be found just to the right of the bus riser. If fitted, the 82C480 will be close to the 82C002.
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Hint Category |
Adapter Cards | |
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Date Created |
08-09-95 | |
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Last Updated |
10-02-99 | |
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Revision Date |
10-02-2000 | |
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Brand |
IBM Aptiva | |
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Product Family |
PS/1 | |
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Machine Type |
2133, 2155, 2168 | |
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Model |
all | |
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TypeModel |
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Retain Tip (if applicable) |
N/A | |
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