Chapter 1. Product Overview
Figure 1–7 Host I/O Module
Host Out 
Host In
CTR
UPS
SHR-1036
The front panel of the host I/O module contains two 68-pin VHDCI SCSI con- nectors and two 9-pin D connectors. The SCSI connectors provide the SCSI bus connections between the adapter in the host system and the controller(s) in the Shelf. One of the 9-pin D connectors interfaces the UPS status signals to the controller. The other provides a serial connection between its respective control- ler, the Shelf, and the SWCC configuration/maintenance PC.
The high-density SCSI connectors on the Host I/O module are designated Host In (bottom connector) and Host Out (top connector). Host In provides the SCSI connection for a one-to-four expansion shelf cabinet installation. Cable connec- tions to multiple storage shelves are made through Trilink adapters.
In addition to the front panel connectors, the Host I/O module contains three pas- sive differential SCSI bus terminators that terminate the SCSI bus from the host system. Termination is automatically disabled when a cable is connected to the Host Out connector. The UPS serial connector on the host I/O module (desig- nated CTR 0 and CTR 1) provides shelf status information to the UPS.
NOTE
If you have only one SCSI cable connection to the host I/O module, you must connect the cable to the Host In connector. Do not use any external bus termination. The Host Out connector on the module is used for mid-bus connections in a mul- tiple-host system configuration.