Siemens Simatic S7-400 - DP Address Areas

Interfaces, Networks and Data Communication for the S7-400
5-12
Automation System S7-400 Configuration and Use
A5E0044271 1-02
5.3 Data Exchange via Communication Functions
Introduction
Data exchange via a variety of bus systems, such as MPI and Industrial Ethernet,
PROFIBUS DP or point-to-point connection can be triggered and controlled in the
user program.
You determined the desired functionality for this program-driven communication by
calling a communication function in the user program. This might be a point in time,
the amount of data or the transmission method.
Corresponding communication functions (SFCs, SFBs, loadable FC/FBs) are
available on the S7-400 for data exchange.
SFCs for S7 Basic Communication via an MPI Subnet
You can transmit up to 76 bytes of data via an MPI subnet using these functions. A
connection configuration is not necessary.
SFC Description
SFC 65
SFC 66
X_SEND
X_RCV
Secure transfer of a data block to the communication partner. This
means that data transmission is not completed until the receive
function (X_RCV) in the communication partner has accepted the
data.
SFC 67 X_GET This SFC can be used to read a variable from a communication
partner without having to place a corresponding SFC in the
communication partner.
SFC 68 X_PUT This SFC can be used to write a variable to a communication partner
without having to place a corresponding SFC in the communication
partner.
SFC 69 X_ABORT This SFC can be used to abort an existing link explicitly without
having to transfer data.