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The data exchanged by the instrument are:
Output Data
from instrument (reading)
Addresses
Input Data
to instrument (writing)
Addresses
Gross weight (H – L)
40008-40009 Command Register
40006
Net weight (H – L)
40010-40011 Digital outputs command
40018
Exchange register R1 (H - L)
40051-40052 Exchange register W1 (H - L)
40051-40052
Exchange register R2
40053
Exchange register W2
40053
Status Register 1
40007
Status Register 2
40148
Instrument status
40150
Execution register
40147
Digital inputs status
40017
Digital outputs status
40018
The data received and transmitted via MODBUS-RTU protocol have the following characteristics:
-
1 start bit
-
8 bit of data,
least significant bit
sent first
-
Settable parity bit
-
Settable stop bit
FUNCTIONS SUPPORTED IN MODBUS
Among the commands available in the MODBUS-RTU protocol, only the following are utilised for
management of communication with the instruments; other commands could be incorrectly
interpreted and generate errors or blocks of the system:
FUNCTIONS
DESCRIPTION
03 (0x03)
READ HOLDING REGISTER (READ PROGRAMMABLE REGISTERS)
16 (0x10)
PRESET MULTIPLE REGISTERS (WRITE MULTIPLE REGISTERS)
Interrogation frequency is linked to the communication speed set (the instrument stands by for at
least 3 bytes before starting calculations an eventual response to the interrogation query). The
parameter allows the instrument to respond with a further delay and this directly influences
the number of interrogations possible in the unit of time.
For additional information on this protocol refer to the general technical specifications
PI_MBUS_300.
In general queries and answers toward and from one slave instrument are composed as follows:
FUNCTION 3: Read holding registers (READ PROGRAMMABLE REGISTERS)
QUERY
Address
Function
1st register address
No. registers
2 byte
A
0x03
0x0000
0x0002
CRC
Tot. byte = 8
