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

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Using the Command Interface
67
DP/AS-Interface Link 20E
Release 11/2002
C79000-G8976-C138–04
Job Parameters
Set the parameters for the read_record and write_record jobs as described in
Section 2.4.1. Sending the commands is controlled by the following parameters:
S
Index:
Specifies the data record number = 2
S
Length:
– The length of the data sent (with write_record) depends on the command;
– The length of the data received (with read_record) is indicated by the
DP/AS-i Link 20E using the status nibble.
Commands in the User Program
To work with commands, include the following in your user program:
1. Specify the command call in a send buffer in the user program.
2. Send this job with write_record (record 2) to the DP/AS-i Link 20E.
3. Following this, query the status of command processing in the input area for
binary values (cyclic services – see Section 2.1). The status information is
entered in bits 4 to 7 in the reserved first byte of the DP input area (status
nibble).
4. Various reactions are possible depending on the result of the status evaluation
as shown in the following flowchart (for more detailed information on the
meaning of the status nibble, please refer to Table 3-1).
To complete command processing, you must always sent a read_record job
(data record 2) either to obtain further status information or to receive response
data.