Siemens SIMATIC S5 CP 523 Manual page 12

System Overview
Communications Mode
In "Communications mode", the CP 523 can communicate over the 1/0 interface with an 1/0 unit
(terminal, CP 523, CPU 944, etc.) equipped with a V.24 (RS 232C) or TTY interface. This mode
enables the transfer of data frames between the CPU and an 1/0 device connected to the CP 523.
The CP 523 provides a total of three communication control procedures, i.e. two protocol-free
procedures and one with a standardized protocol:
. Protocol-free data transmission
- Transparent mode, i.e. data transmission without receiver-side end identifier sequence
- Interpretive mode, i.e. data transmission ~receiver-side end identifier sequence.
. Data transmission with protocol
-3964 (R) mode
Your application program determines the modes you want to use.
You can also evaluate the module's real-time clock in your program for date and time-dependent
tasks.
The FE 200 "SEND" and FB 201 "RECEIVE" function blocks allow user-friendly bidirectional
transfer of message frames with a length of up to 256 bytes. A thorough description, with
examples, is given of how to use the function blocks.
If you decide to forego the convenience of the FB 200 and FB 201 function blocks in favour of
higher data transmission speeds, you can communicate with the CP 523 direct from the user
program. This method of data exchange is also described in detail with examples.
Figure 1-2. S5-115U Programmable Controller with CP 523 and Terminal
1-2
523
CP
EWA4NEB811 6044-02a