Consistency Rules For Sfb 15 “Put” Or Write Tag; Data Transmission Without Data Consistency - Siemens SIMATIC S7-400H Manual

Installation of a CPU 41x-H
Consistency Rules for SFB 15 "PUT" or Write Tag
Using SFB 15 "PUT" data are transmitted consistently if you adhere to the
following consistency rules:
• Active CPU (data sender): Write the receive area in the OB by calling SFB 15
or – if this is not possible – write the send area when the processing of SFB 15
is completed.
• Active CPU (data sender): Write only as much data to the send area as the
block size of the passive CPU (data receiver) specifies.
• Passive CPU (data receiver): Read the received data from the receive area
using an interrupt block.
The following is an example of a situation in which consistent data transmission
cannot be ensured because it violates the second consistency rule: 64 bytes are
sent although the block size of the passive CPU (data receiver) is only 32 bytes.
Active CPU with SFB PUT or write tag
(data sender)
16 Byte
1
16 Byte
2
Send
Range
16 Byte
3
16 Byte
4
Figure 4-10

Data transmission without data consistency

Consistent transfer of larger data blocks spanning several tags can be ensured in
the user program of the S7-400 using SFC 81 "UBLKMOV" (uninteruptable block
move).
These data can be consistently accessed using SFB 14 "GET", SFB 15 "PUT or
reading/writing the tag, for example.
4-44
4 3 2 1
User data
Data transmission
Passive CPU
(data receiver)
32 bytes
32 bytes
4 3 2 1
User data
Automation System S7-400H Fault-tolerant Systems
Receive
Range
A5E00068197-07