Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL - Manual (Page 76)

4–28 Planning an Application
Publication 2706-817
When data entry handshaking is used, the controller logic is required
to set the handshake tag bit before the user-defined handshake
timeout occurs. If the terminal does not receive the handshake bit
before time expires, it will display a handshake timeout message.
The terminal operator must acknowledge the timeout message before
the application can resume. See page 10–16 to adjust the timeout
time.
Example of handshaking with Entry Variables:
Operator enters
value.
Handshake Tag = 0
Operator presses
Enter key.
Terminal Sets Notification Tag = 1
Handshake Tag = 0
Notification Tag = 0
Controller ladder logic program
Verifies that notification address is set to 1.
Sets handshake address to 1.
–
–
Controller program then clears handshake tag.
➁
➂
➃
Controller Sets Handshake Tag = 1
Notification Tag = 1
Handshake Tag = 0
Notification Tag = 0
Message contains an Entry Variable.
➀
➄
Handshake Tag = 0
Notification Tag = 0
Terminal clears notification tag.
Notification Tag Handshake Tag
B3
1 1
B3
WHEN THE TERMINAL SETS THE NOTIFICATION TAG, IT WAITS FOR THE CONTROLLER TO SET THE
HANDSHAKE TAG.
IF THE HANDSHAKE TAG IS NOT SET BEFORE THE SPECIFIED TIMEOUT TIME, THE TERMINAL NOTIFIES
THE OPERATOR THAT THERE IS A COMMUNICATIONS PROBLEM.