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
Page 33 of 46
All rights reserved. Passing on and copying of this document, use and communication of its contents not permitted without written authorization.
6.4
Modbus Framing
Modbus Message Format is as bellow:
Address
Function
Data
Check
8-Bits
8-Bits
N * 8-Bits
16-Bits
6.4.1
Address Field
The address is the beginning of the frame and consists of 8-bits
(1-247). These bits indicate the user assigned address of the slave
device that is to receive the message sent by the attached master.
Each slave must be assigned a unique address and only the
addressed slave will respond to query that contains its address.
When the slave sends a response, the slave address informs the
master which slave is communicating.
6.4.2
Function Field
The function code field tells the addressed slaves what function to
perform. Table lists the function code, all measuring and action that
initiated.
Table 6-2: VP-1405A Modbus Function Codes
Code
Meaning
Action
3 (03H)
Read holding data
Obtain current binary value in one or more
registers
4 (04H)
Read input data
Obtain current binary input status in one or
more registers
6 (06H)
Preset single - register
Place specific binary value into one
16 (10H)
Preset multiple - register
Place specific binary value into a series of
consecutive multiple – registers
6.4.3
Data field
The data field contains information needed by the save to perform
the specific function or contains data collected by the slave response
to query. This information may be values, address references, or
limits. For example, the function code tells the slave to read a
register, and the data field is needed to indicated which register to
start at and how many to read. The imbedded address and data
