Siemens DP/AS-Interface Link 20E, Руководство пользователя

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Using the Command Interface
122
DP/AS-Interface Link 20E
Release 11/2002
C79000-G8976-C138–04
3.3.30 Read_AS-i_Slave_ID_String
Purpose
With this call, an identification string complying with the AS-i slave profile 7.4 can
be read from the AS-i slave with the AS-i slave address specified in the send
buffer. The AS-i master supplies up to 221 bytes of response data. The number of
ID bytes actually sent by the AS-i slave is signaled by the AS–i master in byte 0 of
the receive buffer (number of ID bytes).
If the AS-i slave sends a string longer than 220 bytes, the AS-i master aborts the
string transfer and terminates the job with an error. The received data are then not
made available to the user program.
As long as the string transfer is active, there is no user/analog data exchange with
the addressed AS-i slave.
Note
As an exception, with this call, the bytes contained in the bits “Follows” and “Valid”
are also transferred (see AS–i slave profile 7.4).
Structure of the Job Data in the Send Buffer
Byte Meaning
0 Command number 42
H
1 Slave address
Structure of the Response Data in the Receive Buffer
Byte Meaning
0 Number of ID bytes
1 String byte (1)
2 String byte (2)
... .....
... String byte (n-1)
... String byte (n)
Maximum value for n=220