Motorola MVME2600 manual Scsi Interface, Scsi Termination

Block Diagram

SCSI Interface

The MVME2603/2604 VME module supports mass storage subsystems through the industry-standard SCSI bus. These subsystems may include hard and floppy disk drives, streaming tape drives, and other mass storage devices. The SCSI interface is implemented using the Symbios 53C825A SCSI I/O controller at a clock speed of 40 MHz. The SCSI I/O controller connects directly to the PCI local bus.

The MVME2603/2604 routes its SCSI lines through the P2 connector to the MVME712M transition module (as illustrated in Figure 1-21 on page 1-47). The SCSI control lines have filter networks to minimize the effects of VMEbus signal noise at P2.

The SCSI bus is 16-bits wide in systems that support the VME64 extension (that is, those equipped with 5-row, 160-pin VME backplane connectors). The SCSI bus is 8-bits wide in VME systems that do not support the extension. Refer to the MVME712M User’s Manual, listed in Appendix D, Related Documentation, for the pin assignments of the SCSI connectors used on the transition module. Refer to the Symbios 53C825A data manual for detailed programming information, also listed in Appendix D, Related Documentation.

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SCSI Termination

The individual configuring the system must ensure that the SCSI bus is properly terminated at both ends.

In MVME712M I/O mode, the MVME2603/2604 base board uses the sockets provided for SCSI bus terminators on the P2 adapter board used with the MVME712M. If the SCSI bus ends at the adapter board, termination resistors must be installed there. +5V DC power to the SCSI bus TERMPWR signal and termination resistors is supplied through a fuse located on the adapter board.

In MVME761 I/O mode, the P2 adapter board used with the MVME761 has a jumper to enable/disable SCSI bus terminators. +5V DC power for SCSI termination is supplied through a polyswitch located on the adapter board.

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