Rockwell Automation 2706 DL40 HARDWARE USER MANUAL - Manual (Page 121)

Chapter 10
Using Remote I/O
10 – 29
To accomplish this, the Handshake feature uses an input and output bit in the
PLCs I/O Image Tables. The DL40 will automatically toggle the input
Handshake Bit to its opposite state (0 to 1 or 1 to 0).
To select the Handshake feature, enable (set ON) Switch 7 of DIP Switch
Bank # 2.
You should consider using the Handshake feature when:
•
a large number of Remote I/O devices are involved in an application,
•
a large number of block transfers are in your PLC program,
•
the PLC application is large,
•
the PLCs updates to discrete I/Os may increase the program scan time.
•
ASCII data is to be input using block transfers.
Important: To use the Handshake feature with discrete transfers, the PLC
program must have a rung that accepts the handshake bit and allows
communications to continue. If you have selected the Handshake feature, the
PLC program must contain this rung or the DL40 will not operate properly.
If the DL40 does not detect the handshake for one minute, it will display the
following message:
NO PLC HANDSHAKE
Figure 10.8
Ladder Logic Discrete Handshake and Block Transfer Handshake Rungs
Input Handshake Bit Output Handshake Bit
17 17
CONTINUOUS N
BTR BTW
ENABLE ENABLE
BLOCK TRNSFR READ
RACK
GROUP
MODULE
CONTROL BLOCK
DATA FILE
LENGTH
CONTINUOUS N
BLOCK TRNSFR WRITE
RACK
GROUP
MODULE
CONTROL BLOCK
DATA FILE
LENGTH
BTR BTW
ENABLE ENABLE
BTR
Block Transfer Handshake Rungs Block Transfer Handshake Rungs
BTW