RSTi is Emerson's remote and distributed I/O platform — a family that spans three physical form factors unified by the same configuration philosophy: move the I/O out of the control cabinet and closer to the sensors and actuators. The RSTi-EP slice I/O modules (11.5 mm wide per slice, 48 Mbps system backplane) connect to the controller over PROFINET, EtherCAT, Modbus TCP, or PROFIBUS by swapping a single network adapter module at the head of the slice — the I/O modules themselves are protocol-agnostic. The RSTi-OM IP67 modules mount directly on the machine frame, connected by armored M12 cables, with IO-Link v1.1 master functionality and simultaneous PROFINET, OPC-UA, and MQTT communication. Safety I/O modules within the RSTi-EP family achieve SIL 3/PLe Cat.4 ratings and share the same backplane, same power bus, and same Ethernet cable as the standard I/O — safety is integrated into the slice, not wired as a separate relay-based circuit. The common thread across all RSTi form factors is the cabinetless philosophy: every RSTi module is designed to operate without a protective enclosure beyond its own housing.

Cabinetless I/O: the architectural shift

Traditional machine I/O architecture places all I/O modules in a central control cabinet and runs individual sensor and actuator cables — often 50 to 100 conductors — through cable ducts from the cabinet to the field devices distributed across a 20-meter-long machine frame. RSTi inverts this: small I/O blocks are mounted at multiple points along the machine, each serving the sensors and actuators within a few meters. The sensor cables shrink from 20 meters to 2 meters. The cable duct from the cabinet shrinks from a 100 mm × 60 mm trunk to a single Ethernet cable and a single 24 VDC power cable daisy-chained between RSTi stations. The control cabinet itself shrinks — from a two-door enclosure housing the PLC plus all I/O to a single-door enclosure housing only the PLC, the main power distribution, and the network switch. For a machine builder, the savings are in cable, cabinet steel, panel labor, commissioning time (fewer miswired terminals), and troubleshooting time (a diagnostic LED on the RSTi module points to the exact port with the fault, instead of tracing a wire number through 20 meters of duct).