Siemens SIMATIC S5 CP 523 Manual page 179

Communications Mode
CPU user program
CPU issues "Receive message" request
Word 0 Word 2
Job No. Not
A080 significant
H
CPU reads coordination information
Word 2
Word 0
Coordination
Message
information
and CBR:
length
Coordination
(in bytes)
byte 'receive'
*
If no message frame in
Receive mailbox, end here!
CPU reads 1st message block (8 bytes)
Word 0 Word 2
Data Data
CPU reads further message blocks (8 bytes each)
Word 0 Word 2
Data Data
CPU reads last message block ( 8 byte)
Word 0 Word 2
Data Data
* Relevant only in 3964(R) mode.
Figure 7-14. Transfer Memory Assignments for "Receive Message Frame"
7-74
Word 4
Not
significant
Word 4
Not Byte 6/byte 7:
signifi- No. of message
frame
cant blocks/No. of
CPU writes word 0
Word 4
Data
CPU writes word 0
Word 4
Data
CPU writes word 0
Word 4
Data
Word 6
Not
significant
Word 6
message
frames
8-byte
trans-
Word 0
fer
Data
memo-
ry in
CP 523
Word 6
Data
Word 0
Data
Word 6
Data
Word 0
Data
Word 6
Data
CP functions
CP reads job request from
transfer memory and writes
coordination information
into transfer memory
CP transfers 1st message
block from Receive mailbox
to transfer memory
CP transfers further
message blocks from
Receive mailbox to transfer
memory
CP transfers last message
block from Receive mailbox
to transfer memory
EWA 4NEB 811 6044-02a
CP 523