Specifications

4
Technical Description Section 1-2
- No configuration required within the PLC.
- The PU protocol is handled entirely by the firmware of the PLC. A PLC program
(function blocks, etc.) in the PLC is not required to handle the communication.
- The protocol provides error control. Transmission errors are detected and, if pos-
sible, eliminated by repeating the transmission. An electrically isolated, noise-
immune interface hardware in accordance with the 20 mA current loop interface
standard permits the application even in a harsh industrial environment.
- The parameters of the interface SER1 are assigned in the programming soft-
ware in a protocol-specific manner and are stored in the application description.
The parameters can also be modified in the setup mask or any other I/O mask of
the terminal.
- The programming system provides a maximum of support to the operator in
programming the operating terminal. The definitions (abbreviations) used here
are identical with the definitions used within the PLC program.
1.2 Technical Description
The PU protocol is used to connect the operating terminal to the Siemens PLCs.
The PU protocol AS511 allows random read and write access to all PLC data. Any
byte-structured data types can also be accessed in bit-mode. The size of the ad-
dress area depends on the respective PLC.
Access to the individual bytes of a data word within a data block is also possible.
A read access must be performed before individual bits or bytes of a data word
within a data block can be accessed for a write operation. Subsequently, a write
access is possible to the entire data structure. When accessing individual bits or
bytes, special care needs to be taken to ensure that neither the terminal nor the
PLC modify individual bits within one byte (or individual bits within one data word,
respectively).
1.3 Protocol Parameters Siemens PU AS511
To ensure proper communication, the parameters must not be altered.
Baud rate: 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 375000,
500000 Baud
Parity: none, even, odd
Data length: 5, 6, 7, 8
Stop bits: 1, 1.5, 2
Handshake: no handshake, Hardware, Software
The operating terminal adapts to the default parameters of the PU interface. It is
therefore
not necessary to modify the interface parameters in the PLC. This allows
communication between the operating terminal and Siemens PLC without requir-
ing any configuration.