Chapter 8 Exercising program
8-20
[Figure 8.10] shows interlock program of Read data Function Block. If in normal communication, it allows
TX/RX as in sequence shown in [Figure 8.6] and even in abnormal communication, it allows communication
in the following sequence after waiting for response 1 sec..
[Figure 8.10] Interlock program to Read data
Prepare one program integrated by 4 programs above and let it downloaded to PLC through compile
process, and then run the program to allow communication with dedicated communication slave station in
user defined mode. Identical frame list and program can be also used in Cnet station 2 & 3. And if the
program is run via compile and download, identical communication is available in station 2 & 3.
Remark
[Note1] Waiting time for response shall be set larger enough than max. response time estimated in
consideration of frame length and data transmission speed.
After Read request frame is transmitted, delete RD_START flag
and turn MON_2 flag on which turns on monitoring timer of
Read response frame.
After Read response frame is received, set WR_START flag to
send Write request frame and turn on MON_2 flag so as to stop
1 sec. timer.
If no response is received for 1 sec. after Read
request frame is sent, turn on WR_START to
send Write request frame so as to allow next
frame transmitted even in abnormal state
through this interlock program.