MATRIX HOT SWITCH INTERFACE UNIT IS A COMPUTER CHANGEOVER SWITCH THAT MONITORS THE STATUS OF ACTIVE CC1 IN A 9740/9760 The CM9760-HS hot switch interface unit is a computer changeover switch that monitors the status of an active CC1 in a 9700 Series system. If the active CC1 fails to operate, the hot switch receives an alarm and transfers control to a standby CC1. All devices controlled by the active CC1 are then controlled by the standby CC1. Also, all common computer input/output devices (keyboard, monitor, printer and two serial ports) are switched from the active CC1 to the standby CC1; this can be done when there is a failure or by command of the system user. The hot switch is made up of three subunits: the CCC (computer changeover control), the CPS (computer peripheral switch), and the SEU (serial expansion unit). The CCC is the main component of the hot switch. The data connections between the interfaced CC1s and the hot switch are located on the rear of this unit. The CPS switches computer peripherals so that two CC1s may use only one monitor, printer, keyboard, and standard serial port. The SEU switches the data communications ports. Each SEU can switch 16 standard RS-422/RS-485 ports. The CM9760-HS allows for easy expansion to 128 ports.