Basic Principles of Serial Data Transmission
2.4 Data Transmission with the ASCII Driver
Point-to-point connection CP 440 Installation and Parameter Assignment
Manual, 09/2007, A5E00057742-03
31
2.4.2 Sending Data with the ASCII Driver
Sending Data
When you send data, you specify the number of user data bytes to be transferred in the
"LEN" parameter of the call of the SEND_440 function block.
When you work with the end criterion "Character Delay Time" when receiving data, the
ASCII driver pauses between two message frames when sending. You can call the
SEND_440 FB at any time, but the ASCII driver does not begin its output until a period
longer than the configured character delay time has elapsed since the last message frame
was sent.
If you work with the "End-of-Text Character" criterion, you have a choice of three options:
● Send up to and including the end-of-text character
The end-of-text character must be included in the data to be sent. Data is sent only up to
and including the end-of-text character, even if the data length specified in the FB is
longer.
● Send up to length configured at the FB
Data is sent up to the length configured at the FB. The last character must be the end-of-
text character.
● Send up to the length configured at the FB and automatically append the end-of-text
character or characters
Data is sent up to the length configured at the FB. The end-of-text character(s) is/are
automatically appended; in other words, the end-of-text characters must not be included
in the data to be sent. 1 or 2 characters more than the number specified at the FB are
sent to the partner, depending on the number of end-of-text characters.
When you work with the end criterion "fixed frame length", the number of data bytes
transferred in the send direction is as specified for the "LEN" parameter of the SEND_440
FB. The number of data bytes transferred in the receive direction, i.e. in the receive DB, is as
specified at the receiver using the "fixed message frame length" parameter in the parameter
assignment interface interface. The two parameter settings must be identical, in order to
ensure correct data traffic. If an end code is not detected when data is sent, a pause equal to
the length of the monitoring time is inserted between two message frames to allow the
partner to synchronize (identify the beginning of the message frame).
If some other method of synchronization is used, the pause in sending can be deactivated by
means of the parameter assignment interface.
Note
When XON/XOFF flow control is configured, the user data must not contain the configured
XON or XOFF characters. The default settings are DC1 = 11H for XON and DC3 = 13H for
XOFF.
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