Comtrol Modbus TCP Quick Start User Manual
Page 42
42 - Configuring Read/Write Raw/ASCII Devices
DeviceMaster UP Modbus/TCP Quick Start: 2000477 Rev. G
Configuring Read/Write Raw/ASCII Devices
i.
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.
j.
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.
k. 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.
l.
Set the Use Maximum Sized Modbus Messages option if you are receiving messages over 196 bytes, your
PLC can receive messages larger than 200 bytes, and you want to decrease latency and network
usage.
m. Set the PLC Tx Data Address to the PLC memory address at which to request the transmit data
message. This 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.
n. Set the PLC Tx Poll Rate to the rate at which you would like the DeviceMaster UP to poll for transmit
messages. If Tx Sequence Number Syncing is disabled, this rate must be faster than the rate at which
you wish to transmit data. If not, transmit messages will be lost.
o.
Set the PLC Tx Poll Message Length to the length in bytes of your longest transmit data packet plus
four bytes for the sequence number and length parameters at the start of the transmit message
(maximum of 250 bytes). Any additional bytes requested will be left unused.
p.
If you wish to enable synchronization of the transmit data messages between the PLC and the
DeviceMaster UP:
-
Enable Tx Sequence Number Syncing Enable.
-
Set the PLC Tx Consumed Sequence Address to the PLC memory address at which you wish the
DeviceMaster UP to write the transmit consumed sequence number. This memory address must
point to a 16-bit word and, like the other address definitions, is base 1. When the Tx Produced
Sequence Number (at the PLC Tx Data Address) and this consumed sequence number are equal, the
DeviceMaster UP has transmitted the last message and is ready for the next transmit message.
Note: Go to Step
on Page 45 to complete configuration.