The standard DeltaV Serial Card supports serial devices that use the Modbus RTU or ASCII protocol. The programmable Serial Card supports custom protocols. Both cards communicate through RS232, RS422/485 half duplex, or RS422/485 full duplex signals. The Serial Cards support both master and slave modes of communications. Master mode is normally used to communicate with a PLC or other third party device supporting the Modbus protocol. In this mode, the Serial Card is the master device on the serial communications link and controls the requesting of data from the other device. Slave mode is used for connection to a Modbus master device. In slave mode, the Serial Card acts as a slave to the connected device responding to data read and write requests issued by the master. The card is capable of emulating up to 16 slave devices on each port. You configure the devices on the port and set them to different slave addresses. If you want a serial card to have one slave address, configure a port with only one device object and create all the datasets under that device. Datasets are described in more detail below.