The main modules in a slave I/O system include the Slave I/O Extender Module (621-9000) and the Slave Power Supply Extender Module (621-9001). The Slave I/O Extender Module extends processor rack I/O to the slave rack, which may be no farther than 50 feet
(15m) from the logic controller. The Slave I/O Power Supply Extender Module extends processor rack power to the slave rack.

The Slave I/O Extender Module resides in the rightmost slot of the I/O rack, and the slot beside it houses the Slave Power Supply Extender Module.

The Slave I/O system requires a parallel I/O cable no longer than 50 feet (15m), unless the Slave Power Supply Extender Module is used. Then, the 628-1600 Slave Power Supply Cable is required instead.