A-Series I/O modules which communicate using ModbusRTU serial protocol. Models ASIO-41xx are "robust", and have an extended operating temperature range.
A Series 16Ch Digital I/O Module (8in/8out) w/ Modbus & LEDs
A Series 15 Channel Digital I/O Module w/ Modbus, Wide Temp
A Series 16 Channel Isolated Digital Input w/ Modbus & LEDs
A Series 12 Channel Sourcing Isolated Digital Output Module with Modbus
A Series 8 Channel Power Relay Output Module with Modbus