Siemens SIMATIC CP 440 Manual page 31

Send data
The figure below illustrates a send operation.
Figure 2-4
Receiving Data with the ASCII Driver
In data transmission using the ASCII driver, you can choose between three
different end criteria when data is received. The end criterion defines when a
complete message frame is received. The possible end criteria are as follows:
On Expiry of Character Delay Time
The message frame has neither a fixed length nor a defined end-of-text
character; the end of the message is defined by a pause on the line (expiry of
character delay time).
On Receipt of One or More End-of-Text Character(s)
The end of the message frame is marked by one or two defined end-of-text
characters.
On Receipt of a Fixed Number of Characters
The length of the receive message frames is always identical.
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
Waiting for
send job
Sending user
data
Sequence of a Send Operation
Basic Principles of Serial Data Transmission
Send job arrived
The amount of data to
be sent is taken from
the LEN parameter of
the send job.
2-13