Siemens SIMATIC S5-115U, User Manual

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S5-115U Manual Communications Capabilities
12.4.2 Coordination Bytes
The ASCII driver monitors data traffic and stores status and error information in two coordination
bytes, SEND (CBS) and RECEIVE (CBR).
Figure 12-11 shows the format of both coordination bytes.
Error message (see Table 12-8)
Error message (see Table 12-8)
Sending permitted
Is set by the user and reset by the ASCII driver when the send procedure is finished. A leading edge at this bit
activates the send procedure.
2
3
2
6
2
5
2
7
2
4
2
2
2
1
2
0
SEND Coordination Byte (CBS) (Flag byte or high-order byte in data word)
RECEIVE Coordination Byte (CBR) (Flag byte or high-order byte in data word)
Receive permitted
Is set by the user and reset by the ASCII driver when the Receive mailbox is full.
2
3
2
6
2
5
2
7
2
4
2
2
2
1
2
0
Figure 12-11. Coordination Byte Format
Note
As long as the "send/receive permitted" bits are set, the location of the Send and
Receive mailboxes (DB or flag area) cannot be changed.
Note
The operating system can set or reset bits in the coordination bytes after every
statement without regard to the PLC cycle. In consequence, multiple scanning of a
coordination bit in a program cycle may produce different results (be careful when
evaluating signal edges)!
EWA 4NEB 811 6130-02b
12-23