User guide

Using Explicit Messaging (PCP Communications)

7-5

7.3.1 PCP Read Message Format

PCP Reads require the following Command and Reply message

formats:

Command

Table 7.3 – Command Message Format

Word Name Description

0 CR The Communication Reference (CR #)

to read from

1 Index The index of the variable to read

2 Sub Index The sub-index of the variable to read

(not used)

Table 7.4 – Reply Message Format

Word Name Description

0 Command

Word Echo

Echo of the Command Word (0004h)

1 Message

Length

Number of words following

2 CR The Communication Reference (CR #)

the Reply is from

3 Result Result Code:

0=Success

FFFFh = Timeout

FFFEh = Out of buffers to store the

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)

5 Data 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

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

data reads