Data Transmission With The Ascii Driver; Principle Of The Data Transmission With The Ascii Driver; Sending Data With The Ascii Driver - Siemens Simatic S7-300 CP 341 User Manual

Basic Principles of Serial Data Transmission

2.6 Data Transmission with the ASCII Driver

2.6 Data Transmission with the ASCII Driver
2.6.1

Principle of the Data Transmission with the ASCII Driver

The ASCII driver controls data transmission via a point-to-point connection between the
communication processor and a communication partner. This driver contains the physical
layer (layer 1).
The structure of the message frames is left open through the S7 user passing on the
complete send message frame to the communication processor. For the receive direction,
the end criterion of a message must be configured. The structure of the send message
frames may differ from that of the receive message frames.
The ASCII driver allows data of any structure (all printable ASCII characters as well as all
other characters from 00 through FFH (with 8 data bit character frames) or from 00 through
7FH (with 7 data bit character frames) to be sent and received.
2.6.2

Sending data with the ASCII driver

Sending data with ASCII driver
For sending, you specify the number of user data bytes to be transferred when the
P_SND_RK function block is called as the "LEN" parameter.
If you are working with the end criterion "Expiration of character delay time", the ASCII driver
pauses between two message frames when sending. You can call the FB P_SND_FK at any
time, but the ASCII driver does not begin its output until a period longer than the assigned
character delay time has elapsed since the last message frame was sent.
If you are working with the "End-of-text character" end 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 assigned in the FB
Data is sent up to the length assigned in the FB. The last character must be the end-of-
text character.
The message frame will be sent without error message even if the data to be sent do not
contain the end-of-text character.
● Send up to the length assigned in the FB and automatically append the end-of-text
character(s)
Data is sent up to the length assigned in the FB. The end-of-text character is
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.
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CP 341 Point-to-Point Communication, Installation and Parameter Assignment
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Manual, 09/2008, A5E02191071-01