Comtrol Modbus TCP Quick Start - Manual (Page 55)

DeviceMaster UP Modbus/TCP Quick Start: 2000477 Rev. G Configuring Read/Write Raw/ASCII Devices - 55
Configuring Read/Write Raw/ASCII Devices
11. Dual Master – Write Mode Only:
Use the following procedure to configure Dual Master - Write mode.
Under the Serial Modbus Master and Modbus/TCP Settings (Raw-Data Only) section:
a. Set the Rx (To PLC) Transfer Mode to Master (Write to PLC).
b. Set the Tx (From PLC) Transfer Mode to Slave (PLC Writes).
c. Set the Maximum Rx Data Packet Size to that of the largest expected receive data packet. This can be a
maximum of 2048 bytes in Master Rx mode.
d. Set the Oversized Rx Packet Handling to either Truncate or Drop, depending how you want to handle
oversized received packets.
e. Set Rx MS Byte First if you want to receive data most significant byte first.
f. Set Tx MS Byte First if you want to transmit data most significant byte first.
g. Set the Disable Non-Filtered To PLC Rx Queue option if you only want to receive the last received data
packet. (If two or more packets are received during the Maximum PLC Update Rate time period, only
the last received data packet will be returned.)
h. Set the Disable Tx Sequence Number Check option if you want to disable the transmit sequence number
checking.
• If selected, the transmit sequence number checking is disabled. All transmit messages will be
transmitted if the sequence number has been incremented or not.
• If not selected, the sequence number is checked and the message will only be transmitted if the
sequence number has been updated.
Under the Modbus/TCP Master Rx/Tx Settings (Raw-Data only) section:
i. Enter the PLC IP Address:
• For Modbus/TCP slaves, set the PLC IP Address to that of your PLC in xxx.xxx.xxx.xxx format.
• For Modbus/RTU or Modbus/ASCII serial slaves, set the PLC IP Address to that of this
DeviceMaster UP in xxx.xxx.xxx.xxx format.
Note: The Modbus serial slave must be attached to one of the serial ports on this DeviceMaster UP
chassis.
j. Enter the PLC Device ID:
• For Modbus/TCP slaves, set the PLC Device ID to that of your PLC. This is typically 1.
• For Modbus/RTU or Modbus/ASCII serial slaves, set the PLC Device ID to that of the serial slave
device.
Note: This must be a unique device id attached to this DeviceMaster UP chassis.
k. Set the PLC Rx Data Address to the PLC memory address where you want to place the received data
message. This address is Base 1, which means the address starts at 1 (or 400001 for some PLCs). If
your address range is Base 0, or starts at zero, you will need to add one to your address.
l. Set the Maximum PLC Update Rate to the fastest rate your PLC can reliably receive and process data.
This is typically longer than the scan rate. The default of 40 milliseconds is usually sufficient, but
your system may require a longer time period.
m. Set the Use Maximum Sized Modbus Messages option if you are receiving messages over 196 bytes, your