Siemens SIMATIC S7-1200

Communication processor and Modbus TCP
13.3 Point-to-point (PtP) communication
S7-1200 Programmable controller
1126 System Manual, V4.2, 09/2016, A5E02486680-AK
13.3.5.7
Receive_P2P (Enable receive messages)
Table 13- 26 Receive_P2P (Receive Point-to-Point) instruction
LAD / FBD
SCL
Description
"Receive_P2P_DB"(
PORT:=_word_in_,
BUFFER:=_variant_in_,
NDR=>_bool_out_,
ERROR=>_bool_out_,
STATUS=>_word_out_,
LENGTH=>_uint_out_);
Receive_P2P checks for messages
that have been received in the CM
or CB. If a message is available, it
will be transferred from the CM or
CB to the CPU. An error returns
the appropriate STATUS value.
1
STEP 7 automatically creates the DB when you insert the instruction.
Table 13- 27 Data types for the parameters
Parameter and type
Data type
Description
PORT IN PORT After you install and configure a CM or CB communication device, the port
identifier appears in the parameter helper drop-list available at the PORT box
connection. The assigned CM or CB port value is the device configuration
property "hardware identifier". The port symbolic name is assigned in the "Sys-
tem constants" tab of the PLC tag table. (Default value: 0)
BUFFER IN Variant This parameter points to the starting location of the receive buffer. This buffer
should be large enough to receive the maximum length message.
Boolean data or Boolean arrays are not supported. (Default value: 0)
NDR OUT Bool TRUE for one execution when new data is ready and operation is complete
with no errors.
ERROR
OUT
Bool
TRUE for one execution after the operation was completed with an error.
STATUS
OUT
Word
Execution condition code (Default value: 0)
LENGTH
OUT
UInt
Length of the returned message in bytes (Default value: 0)
The STATUS value is valid when either NDR or ERROR is TRUE. The STATUS value
provides the reason for termination of the receive operation in the CM or CB. This is typically
a positive value, indicating that the receive operation was successful and that the receive
process terminated normally. If the STATUS value is negative (the Most Significant Bit of the
hexadecimal value is set), the receive operation was terminated for an error condition such
as parity, framing, or overrun errors.
Each PtP communication interface can buffer up to a maximum of 1024 bytes. This could be
one large message or several smaller messages. If more than one message is available in
the CM or CB, the Receive_P2P instruction returns the oldest message available. A
subsequent Receive_P2P instruction execution returns the next oldest message available.