The LN Free Programmable PRG 600 Series Controllers are microprocessor-based free programmable controllers designed to control various building automation systems, such as multi-zone air handling units and central plant applications. The PRG 600 Series controllers use the LonTalk® communication protocol. The PRG 600 Series controllers support up to 2 Input/Output extension modules that operate off of a separate sub-bus, providing the PRG 600 Series controller with up to 40 universal inputs and 36 universal outputs.