Compaq AA-RHGWC-TE manual Communications with the Host Computer, MUC Switch Functions

These tape libraries each have a multi-unit controller (MUC) that serves two functions:

•It is a SCSI adapter that allows the SCSI interface to control communications between the host and the tape library.

•It permits the host to control up to five attached library units in a multi-unit configuration. Multi-unit configurations are not discussed in this manual. For more information on multi-unit configurations, see the TL82X/TL893/TL896 Automated Tape Library for DLT Cartridges Facilities Planning and Installation Guide.

The following sections describe how to prepare these tape libraries in more detail.

8.11.1 Communications with the Host Computer

Two types of communications are possible between the tape library and the host computer: SCSI and EIA/TIA-574 serial (RS-232 for nine-pin connectors). Either method, when used with the multi-unit controller (MUC), allows a single host computer to control up to five units.

A TruCluster Server cluster supports SCSI communications only between the host computer and the MUC. With SCSI communications, both control signals and data flow between the host computer and tape library use the same SCSI cable. The SCSI cable is part of the shared SCSI bus.

An RS-232 loopback cable must be connected between the Unit 0 and Input nine-pin connectors on the rear connector panel. The loopback cable connects the MUC to the robotic controller electronics.

Switch 7 on the MUC switch pack must be down to select the SCSI bus.

8.11.2 MUC Switch Functions

Switch pack 1 on the rear of the multi-unit controller (MUC) is located below the MUC SCSI connectors. The switches provide the functions shown in Table 8–12.

Table 8–12: MUC Switch Functions

Switch	Function
1, 2, and 3	MUC SCSI ID if Switch 7 is downa
4 and 5	Must be down, reserved for testing
6	Default is up, disable bus reset on power up

8–50Configuring a Shared SCSI Bus for Tape Drive Use