Siemens SIMATIC S7 Manual page 34

ID
DB_PARAM
RECV_TIME
CONN_TIME
MODBUS / TCP communication via the integrated PN interface of the CPU
2XV9450-1MB02; Manual edition 2.1
To each connection between the PN PLC and a communication partner a
connection ID is assigned. When operating various connections an individual
ID is required for each logical connection. This connection ID is defined in the
connection parameter block, which is part of the parameter data block
MODBUS_PARAM. The connection ID unambiguously specifies the
connection between the PLC and the communication partner. The ID can be
set to values between 1and 4095.
The connection ID defined in the connection parameter block has to be
entered here and must be unique within the PLC.
The parameter DB_PARAM assigns the number of the data block
MODBUS_PARAM. This parameter data block includes the connection
parameters and the Modbus-specific parameters, which are necessary for the
communication between the PN PLC and the Modbus device.
This parameter is declared in plain text: "DBxy".
The range of values for this parameter depends on the PLC. 0 cannot be
used as a DB number since it is reserved for system functions.
The parameter data block can contain a sequence of parameters for several
connections. It is also possible to use different parameter data blocks for
multiple connections.
The monitoring time RECV_TIME observes the data input from the
communication partner. The shortest adjustable time is 20 ms.
In the operating mode S7 is client, an indication RECV_TIME < 20 ms
causes an error message and the request is rejected. When the time
RECV_TIME elapses, the active request is cancelled with an error.
In order to receive a Modbus telegram, TRCV has to be called twice. With
each call of TRCV, the RECV_TIME is triggered. The monitoring time is
started with the call of TRCV and stopped after the receipt of the telegram
segment.
In the operating mode S7 is server, an indication RECV_TIME < 20 ms
causes the use of the default time of 1,2s. If the monitoring time elapses, an
error is reported. The RECV_TIME monitors the duration of the TCP stream.
The interval between two requests is not taken into consideration.
The monitoring time CONN_TIME observes the connection establishment
and the connection termination. The shortest adjustable time is 100 ms.
When CONN_TIME elapses, the corresponding error code is displayed at the
output STATUS_CONN.
In the operating mode S7 is server, an indication CONN_TIME < 100 ms
causes the use of the default time 5s. This is also true for the operating mode
S7 is client with connect_at_startup = TRUE.
During cyclic operation in the operating mode S7 is client,
CONN_TIME < 100ms causes an error message and the request is rejected.
Function Block MODBUSPN
6-8