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3.934 bytes |
Service Hints & Tips |
Document ID: VLAR-3X9PF6 |
SCSI Adapters - Terminating the IBM SCSI-1 Adapters
Applicable to: World-Wide
Just as ST-506 and ESDI adapters need a terminating resistor (T-RES) on the last drive, so the SCSI adapters must be told where to find the "end of the line."
16-Bit SCSI Adapter
The 16-bit PS/2 SCSI Adapter includes a T-RES terminator chip on the adapter. This chip must remain in the following instances:
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1. |
If no physical devices (also called PUNs, for Physical Unit Numbers) are connected to the adapter, because it is not currently being used. |
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2. |
If the PUNs are all internally attached, or all externally attached. |
The T-RES chip must be removed if internal and external PUNs are attached. In this case in-line terminators (which come with the option cables) are used between the last internal and external PUNs and the cables connecting them to the next-to-last PUNs (or the adapter, if the PUN is the only internal or external device on the chain).
For example, to connect two internal and three external PUNs, the internal devices would be daisy-chained from the internal 50-pin edge-connector, while the external devices would daisy-chain from the 60-pin D-shell connector on the back of the card. If either the internal devices or the external devices are all removed, the T-RES chip would be needed on the adapter. All the terminators needed are included with the various components; however, should the T-RES chip be removed (and lost), but be needed at a later date, a replacement may be ordered as a service part (FRU part number 57F2870).
32-bit SCSI Adapter with Cache
The original 32-bit PS/2 SCSI Adapter with Cache is different in the respect that it does not come with an onboard T-RES chip. There is a separate external terminator (Part number 6451039) which must be used if no external devices are attached. Later shipments of the PS/2 SCSI Adapter with Cache were redesigned to be similar to the PS/2 SCSI Adapter in that it too has an onboard terminator, eliminating the need for an external one. The new adapter can be easily identified by the bright orange terminator on the adapter.
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Hint Category |
SCSI | |
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Date Created |
11-08-98 | |
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Last Updated |
19-11-98 | |
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Revision Date |
18-11-99 | |
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Brand |
IBM Options | |
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Product Family |
SCSI Adapters | |
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Machine Type |
ISA, MCA, PCI, PCMCIA | |
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Model |
All | |
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