Siemens SIMATIC S5 CP 523 Manual page 171

Communications Mode
7.6.2 Sending Message Frames with End-of-Text Character Specification
Specify one or two end-of-text characters with the Send request in word 4. The CP detects the end
of a message frame autonomously through these end-of-text characters.
Note:
The end-of-text characters of the message frame sent by the CPU may differ from the end-of-
text characters configured in parameter block 7 (
in parameter block 7 refer to the message frames received by the CP from a peripheral device.
Procedure for sending message frames with end-of-text characters
1. The CPU transfers the following to the transfer memory.
• The end-of-text characters (word 4)
• Message frame length of 0 bytes (word 2)
• The "Coordinate data transfer for sending message frame" job number (A001
2. The CPU reads the coordination information from word 0 of the transfer memory. If the CP has
not accepted the job (bit 0 ="0"), no message frame can be sent.
3. The CPU transfers the message frame to the transfer memory in message blocks of eight bytes.
Note:
The CP stores the number of message frames in the Receive mailbox in byte 7, so you can also
determine after a Send job whether you can receive a message frame.
Example: Sending a message frame with end-of-text characters 0D0D
Start address 128 is set on the CP. The message frame is stored in DB 20 beginning DW0. Flag 100.1
is set if the CP has accepted the job. The program does not describe how F 100.1 is reset. You could
reset F 100.1 when another job request has been transferred to the CP. FB 123 can be assigned the
relevant parameters. You can choose the start address of the module and end-of-text characters.
They must be specified when the FB is invoked.
Flags
F 100.1
F 100.2
Flag words
FW 242
FW 244
FW 250
FW 252
FW 254
7-66
Table 7-33. Flags Used in FB 123
Meaning
Message frame transmitted
End-of-text character flag set
Data word pointer
Auxiliary data word pointer
Start address
Current address of the transfer memory
End-of-text character
7.3). The end-of-text characters configured
H
CP 523
) (word 0).
H
EWA 4NEB 811 6044-02a