Rockwell Automation 2706-LV2P_LV2R_LV4P_LV4R DL40 PLUS USER MANUAL - Manual (Page 108)

Remote I/O Communications 8–16
Publication 2706-6.1
The Handshake Bit tells the sender (either the DL40 Plus or the
PLC) that the Image Table (either Output or Input) was received.
For complex system configurations, there may not be enough time to
insure that data is received by the PLC. You can use the Handshake
feature to make sure that data is not lost. When activated, the
Handshake feature holds data until the DL40 Plus receives
acknowledgment from the PLC that it has received the data.
The Handshake feature uses an input and output bit in the PLCs I/O
Image Tables. The DL40 Plus 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.
Consider using the Handshake feature when:
•
large number of Remote I/O devices are involved in an
application,
•
large number of block transfers are in your PLC program,
•
PLC application is large,
•
PLCs updates to discrete I/Os may increase the program scan
time.
•
ASCII data is to be input using block transfers.
•
Returning clock data to PLC.
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 selected the
Handshake feature, the PLC program must contain this rung or the
DL40 Plus will not operate properly. If the DL40 Plus does not
detect the handshake for one minute, it will display the following
message:
NO PLC HANDSHAKE
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
Handshake Bit