Linking To Other Systems With Fetch/Write - Siemens S7-300 Configuration Manual

Linking to other systems with FETCH/WRITE

The FETCH and WRITE modes supported on ISO transport connections, TCP, and ISOon-
TCP connections can be used with any other device to access the S7 system memory areas.
To be able to use this type of access, for example for PC applications, you need to know the
PDU structure of the jobs. The required S7 or S5 headers for request and response frames
are 16 bytes long and their structure is described in this chapter.
a) Structure of WRITE frames
The meaning and values of parameters shown without values in the following table can be
found in the section "Parameter values".
WRITE request frame
0
1
2
3
4
5
6
7
8
9
A
B
C
D
I
F
a) Structure of FETCH frames
The meaning and values of parameters shown without values in the following table can be
found in the section "Parameter values".
FETCH request frame
0
1
2
Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13
System ID
Length of header in bytes
ID OP code
Length OP code
OP code
ORG field
Length ORG field
ORG ID
DBNR
Start address
Length
Empty field
Length empty field
Data field up to 64 K
System ID
Length of header
WRITE acknowledgment frame
="S" 0 System ID
="5" 1
=16d. 2 Length of header
=01 3 ID OP code
=03 4 Length OP code
=03 5 OP code
=03 6 Ack field
=08 7 Length ack field
8 Error field
9 Empty field
High byte A Length empty field
Low byte B
High byte C
Low byte D free
=FFh. I
=02 F
FETCH response frame
="S" 0 System ID
="5" 1
=0x10 2 Length of header
C
="S"
="5"
=16d.
=01
=03
=04
=0Fh
=03
=No
=FFh
=07
="S"
="5"
=0x10
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