Basic Principles of Serial Data Transmission
2.6 Data Transmission with the ASCII Driver
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
Manual, 09/2008, A5E02191071-01 63
If you are working with the "Fixed message frame length" end criterion, the amount of data
transferred in the send direction is as specified in the "LEN" parameter of the
FB P_SND_RK. The amount of data transferred in the receive direction, i.e. in the receive
DB, is as specified for the receiver using the "Fixed message frame length" parameter in the
parameter assignment interface. The two parameter settings must be identical, in order to
ensure correct data traffic. A pause equal to the length of the character delay time is inserted
between two message frames when sending to allow the partner to synchronize (recognize
start of message frame).
If some other method of synchronization is used, the pause in sending can be deactivated in
the parameter assignment interface.
Note
When XON/XOFF flow control is assigned, the user data must not contain any of the
assigned XON or XOFF characters. The default settings are DC1 = 11H for XON and
DC3 = 13H for XOFF.
Sending data
The figure below illustrates a send operation.
6HQGUHTXHVWDUULYHG
5HTXHVWSURFHVVHG
:DLWLQJIRU
VHQGUHTXHVW
6HQGLQJ
XVHUGDWD
7KHDPRXQWRIGDWDWR
EHVHQWLVWDNHQIURP
WKH/(1SDUDPHWHURI
WKHVHQGUHTXHVW
Figure 2-20 Flowchart of a send operation
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