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VP-1405A Advanced Power Chapter 6 - Protocol and Communication
V-PM1000 Series, Veesta Power Module Product Series
48V Power Supply & Charger Instructions & User's Manual
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Item Convention
Slave Address 1 Character
Function Code 1 Character
Data field N Characters
Error Check 16 bit CRC
End of Frame
silence on line for time
≧
4 characters
6.3.1 Slave Address
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-1405A the salve address can be from 1 to 247.
6.3.2 Function Code
This is a second byte of every transmission. Modbus® defines
function codes of 1 to 127. The VP-1405A 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.
6.3.3 Data
This will be a variable number of bytes depending on the function
code. This may be actual values, set-points, or addresses ... sent
from the master to the slave or from the slave to the master.
6.3.4 CRC
This is a two-byte error checking code.
6.3.5 Protocol
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
means of checking for errors. No response is transmitted if any error
has occurred.