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ENCLOSED I - MODBUS PROTOCOL
Electrical connection
MODBUS supporti s accessed by RS485 port (connector M16).
Terminals are defined accordingly to standard RS485:
M16-1.......GND
M16-2.......D- (inverting terminal)
M16-3.......D+ (non inverting terminal)
When there is no communication and the connector is open there is a positive voltage 3÷5V between terminal D+ and terminal D-, a sit should
be for the other terminal which has to be connected.
On RS485 bus may reside 32 dispositive (for example other Sentinel PRO devices) one of them is the one that supervise (for example a Per-
sonal PC or a PLC) which functions as the master MODBUS
Since all the dispositive one the same bus can be accessed, their MODBUS address has to be properly configured, specifically two slave units
connected to the bus cannot have the same address otherwise they will both be inaccessibly.
On Sentinel Pro MODBUS address can be configured in menu 6 (parameter 6-3), default is 1.
Normally PC are not provided with RS485 serial port while there could be a RS232 (COM port). Hence a converter USB/RS485 or RS232/
RS485 is required.
A converter which has been tested for compatibility with Sentinel PRO is: USB-RS485-WE-1800-BT produced by FTDI distributed by many
electronic vendors (RS, Digikey, Farnell, etc...).
Serial Interface configuration
Serial Interface has to be configured as follows:
Communication Protocol
General
Mode MODBUS RTU is supported, and the official site (Modbus Specifications) is the reference with particular indication for: Modbus Serial
Line Protocol and Implementation Guide V1.02 e Mosbus Application Protocol V1.1b.
The only implemented function 0x03(3 dec) "Read Holding Registers" in order to read the single registers or contiguous register's blocks.
MODBUS object write access is NOT supported nor possible.
Accessible data are grouped in blocks. All data belonging to the same block have MODBUS address with same high part (more significant
byte) which is also equal to block number.
In the following chapter all blocks and their data are described.
Each described data may be singularly read. Contiguous data may be read with unique transaction referring to the first data address and to
the length sum of the other data. Each block may be interely read with a unique reading transaction. Ex. To read the general parameters block
(Block 1, refer to the description in the following pages) address will be 0x0100 and word number will be 0x0133.
Read transaction example
In order to read the data "Release Firmware", register 0x000B(11 decimal), in blocko 0, MODBUS data reading request and related reply are
represented in the following table:
56
W3-0A5 12-I
Speed
9600 bit/sec
Bit number
8
Parity
No
Stop bit
1
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