Handshake bit, No plc handshake – Rockwell Automation 2706-LV2P_LV2R_LV4P_LV4R DL40 PLUS USER MANUAL User 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

CONTINUOUS N

BTR

BTW

ENABLE

BLOCK TRNSFR READ

RACK

GROUP

MODULE

CONTROL BLOCK

DATA FILE

LENGTH