Siemens SIMATIC S5-115U, Руководство пользователя

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S5-115U Manual Communications Capabilities
Receiving Data
Receive data is automatically entered in interface SI 2's input buffer (buffer size: 1024 bytes) if the
buffer can accommodate it. If it cannot, an error is flagged in the CBR (see Table 12-20).
Bit 7 must be set in the CBR via the application program in order for this data to be forwarded to
the Receive mailbox. The driver automatically enters the number of bytes received in the first
word of the Receive mailbox, and resets bit 7 in the CBR when the mailbox is full. If the data could
not be received without error, an error code is entered in bits 0 to 6 of the CBR; the meanings of
the various error codes are listed in Table 12-20.
Since several different errors can occur, the driver assigns them priorities. The CBR always contains
the code of the error that had the highest priority when the last attempt to receive the data was
made. In Table 12-20, 0 indicates the highest and 6 the lowest priority.
Figure 12-21. Structure of the CBR
Coordination Byte for Receive (CBR)
Receiving is
permitted
when this bit is set Error code (see Table 12-20)
Bit 7 Bit 1 Bit 0
EWA 4NEB 811 6130-02b
12-51