Comtrol Modbus TCP User Guide - Manual (Page 11)

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 1. Introduction - 11
Modbus/TCP Multi-Mode Connectivity
1.4.4. Modbus/TCP Multi-Mode Connectivity
The Modbus/TCP firmware 5.x supports the following Modbus/TCP communication modes:
• PLC Master/DeviceMaster UP Slave Mode on Page 11
• PLC Slave/DeviceMaster UP Master Mode on Page 11
• Dual Master (Virtual Peer-to-Peer) - Write Mode on Page 12
• Dual Master (Virtual Peer-to-Peer) - Read Mode (Dual Polling) on Page 12
• Filtering and Data Extraction Functionality (Patent Pending) on Page 13
1.4.4.1. PLC Master/DeviceMaster UP Slave Mode
PLC Master/DeviceMaster
UP Slave mode:
• Standard Modbus
master to slave device
method of
communication. All
read and write
messages are initiated
by the Modbus master.
• Raw/ASCII, Modbus/
RTU slave, and
Modbus/ASCII slave
devices are supported in
this mode.
• For raw/ASCII mode, the Receive Transfer mode and Transmit Transfer mode are both set to Slave (In
Modbus/RTU-to-Slaves and Modbus/ASCII-to-Slaves mode, the DeviceMaster UP port only operates in
To-Slave mode.
1.4.4.2. PLC Slave/DeviceMaster UP Master Mode
PLC slave/DeviceMaster UP
master mode:
• The DeviceMaster UP
initiates all read and
write messages.
• The DeviceMaster UP
writes received serial
and/or Ethernet device
data directly into PLC
memory with minimal
latency.
• The DeviceMaster UP
polls the PLC for transmit data for serial and/or Ethernet devices.
• PLC programs can be simplified to eliminate both polling for received data and sending of write messages
to transmit data.
• Only raw/ASCII devices are supported in this mode.
• The DeviceMaster UP Receive Transfer mode and Transmit Transfer mode are both set to Master.