Rockwell-automation 20-COMM-I Interbus Adapter Manual de usuario descargar pdf (Pagina 67)

Using Explicit Messaging (PCP Communications) 6-5

The ladder example used in this manual performs PCP Reads and PCP

Writes.

PCP Read Message Format

PCP Reads require the following Command and Reply message formats:

Command

Word Name Description

0CR The Communication Reference (CR #) to read from

1Index The index of the variable to read

2 Sub Index The sub-index of the variable to read (not used)

Word Name Description

Command

Word Echo

Echo of the Command Word (0004h)

Message

Length

Number of words following

2CR The Communication Reference (CR #) the Reply is from

3 Result

Result Code:

0=Success

FFFFh = Timeout

FFFEh = Out of buffers to store the reply

FFFDh = Invalid CR

FFFCh = Could not connect to device with CR

FFFBh = Reply of Command bigger than buffer

4 Data Length The # of bytes of data following (1, 2 or 4 bytes)

5Data Word 1

Contains 8-bit (1 byte) data reads (stored in the high byte),

16-bit (2 byte) data reads, and the most significant word for

32-bit (4 byte) data reads

6Data Word 2 Least significant word for 32-bit (4 byte) data reads

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Rockwell-automation 20-COMM-I Interbus Adapter Manual de usuario Pagina 67