Pentax DSI-200 Series User Manual page 153

A device is the master (can be a PC, a PLC or an HMI) and initiates
communication to perform parameter read or write operations on
slaves. The other devices (slaves) provide data to respond to query
or operations from the master. At the same moment, either the
master or the slave transmits data and the other can only receive
data. The address range of the slaves is 1 to 247, and 0 is broadcast
address. A slave address must be unique in the network.
(2)Transmission mode
The asynchronous serial and half-duplex transmission mode is
used. During asynchronous serial communication, data is sent
frame by frame in the form of message. In Modbus-RTd protocol,
an interval of at least 3.5-byte time marks the end of the previous
message. A new message starts to be sent after this interval.
The communication protocol used by the drive is the Modbus-
RTd slave communication protocol, which allows the drive to
provide data to respond to "query/command" from the master or
execute the action according to "query/command" from the
master.
The master can be a PC, an industrial device, or a PLC. The
master can communicate with a single slave or send broadcast
messages to all slaves. When the master communicates with
a single slave, the slave needs to return a message (response) to
153