Slave Address; Function Code; Data; Crc - Veesta World V-PM2000 Series User Manual

VP-2040 Enhanced IED
V-PM2000 Series, Veesta Power Measurement
Instructions & User's Manual
8.3.1

Slave Address

8.3.2

Function Code

8.3.3

Data

8.3.4

CRC

8.3.5

Protocol

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Item
Slave Address
Function Code
Data field
Error Check
End of Frame
This is the first byte of every transmission. This byte response the
user assigned address of the slave device that is to receive the
message sent by the master. Each slave is started with its address.
In a master request transmission the slave address represents the
address of the slave that is sending the response.
In the VP-2040 the salve address can be from 1 to 247.
This is a second byte of every transmission.
function codes of 1 to 127. The VP-2040 implements some of these
functions. In a master request transmission the function code tells the
slave what action to perform. In a slave response transmission, if the
function code sent from the slave is 1 (i.e. if the function code > 127),
then the slave did not perform the function as requested and is
sending an error or exception response.
This will be a variable number of bytes depending on the function
code. This may be actual values, setpoints, or addresses ... sent
from the master to the slave or from the slave to the master.
This is a two-byte error checking code.
When the master message sent to the assigned slave, it wire enter to
the addressed device through a similar "port". The addressed device
removes the envelope, reads the message, if no errors occurred and
performs the requested task and then replaces the message into the
slaved envelope and "returns to sender".
The information in the response message is the slave address, the
action performed, data acquired as a result of the action, and a
Chapter 8 - Protocol and Communication
Convention
1 Character
1 Character
N Characters
16 bit CRC
silence on line for time
≧
4 characters
Modbus® defines
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