Siemens SIMATIC S5 CP 523 Manual page 178

CP 523
* 5.2
EWA 4NEB 811 6044-02a
START
CPU forwards a "Receive message" request to
CP's transfer memory (word 0*)
CPU reads transfer memory and evaluates
coordination information and coordination
byte (word 0).
message frame in
the Receive mailbox?
(bit 7 in byte 1= 1)
CPU writes word 0
CP transfers data from Receive mailbox
to transfer memory
CPU reads message block
from CP's transfer memory
Read further
Yes
message blocks from
transfer memory?
END
Figure 7-13. Schematic for "Receive Message"
Is a
No
Yes
No
Communications Mode
7-73