5 MODBUS RTU Protocol communication
CP340/CP341/CP440/CP441 Communication and Programming
Entry-ID: 88867653, V1.0, 02/2014
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example
REQ
trigger bit of Send Data, rising edge trigger, which is M0.0 in this
example
DB_NO
Send Data block number, which is 1(DB1) in this example
DBB_NO
Start address of Send Data, which is 0(DB1.DBB0) in this example
LEN
Length of send data, which is 6 in this example
R_TYP
"X" refers to extended data block, which must be in capital form here.
R
Cancel communication, which is not available in this example
DONE
send complete bit, which is TRUE if Send completes and has no error
ERROR
error bit, TRUE indicating that it has an error
STATUS
Status word, ID error code. See Modbus Master Manual - Chapter 7 for
related description.
Other
parameters
Not applicable in this example.
Table 13: Parameter definition of FB8 P_SND_RK
Fig. 90: Invoke FB8 P_SND_RK from OB1
4. Invoke Receive Function Block FB7 P_RCV_RK from Libraries -> CP PtP ->
CP341 and distribute instance data block DB7 to it. Set LADDR as the input
start logic address 256 in hardware configuration.