The Serial Link Selector Module (SLS), model 621-9928R, is a double wide module installed in slots B and C of one I/O card file per Serial I/O System in a redundant configuration. The SLS serves as a general purpose switching device and switches serial communication devices shared by the redundant Logic Managers processors.

The SLS’s only connections to the I/O card file backpanel are the +5 Vdc supply, ground, and the power fail signal. All other are made through the front panel connectors. The state of the SLS’s bus selector circuitry is controlled by the Redundancy Control Module (RCM), that sends a switch select output signal to the SLS through the two 3-position front panel connectors.

Two 12-position detachable screw terminals, labeled A and B, connect to the ports in Logic Managers card files A and B, respectively. Terminals 1 through 8 of the connector are communication signal terminals, and terminals 9 through 12 are dedicated for cable shield connections. A third 12-position terminal, labeled Out, connects to a serial device such as a host computer or Loader/Terminal.

Two LEDs indicate which Logic Manager processor, A or B, is connected to the serial device.