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SUPPORTEd FUNCTIONS
Function
Description
01 (01)
READ COIL STATUS (Reading the state of the logic outputs)
02 (02)
READ INPUT STATUS (Reading the state of the logic inputs)
03 (03)
READ HOLDING REGISTERS (Reading the programmable registers)
04 (04)
READ INPUT REGISTERS (Reading the “read only” registers”)
05 (05)
FORCE SINGLE COIL (Writing the status of each output)
06 (06)
PRESET SINGLE REGISTER (Writing a programmable register)
15 (0F)
FORCE MULTIPLE COILS (Multiple writing of outputs)
16 (10)
PRESET MULTIPLE REGISTERS (Multiple writing of registers)
The values in brackets are the hexadecimal representation of decimal values.
Each single function is explained in detail on pages 34, 35 and 36 of the operator’s manual.
Each function is composed by a Query (request master instrument) and a Response (answer
instrument master). Queries and responses are composed by a sequence of data that are briefly
explained here below (***), please note that the code “0x” before any value indicates that the value
is represented as hexadecimal value.
Besides, all the Modbus addresses have to be represented as hexadecimal values, but, only for
these addresses, there is an important rule to be taken into consideration:
Before converting the address into an hexadecimal value, the 1st digit on the left has not to be
considered and the remaining 4 digits have to be decremented by “1”.
1st EXAMPLE:
To represent the address 40150 (“display division” ) as hexadecimal value, exclude the digit “4”
(remains “0150”), then decrement by 1 the number “0150”. The result is “0149”, now perform the
conversion into hexadecimal. The result is “00 95”. This is the value to be used in the query.
2nd EXAMPLE:
To represent the address 40402 (“analog outpu type” ) as hexadecimal value, exclude the digit “4”
(remains “0402”), then decrement by 1 the number “0402”. The result is “0401”, now perform the
conversion into hexadecimal. The result is “01 91”. This is the value to be used in the query.
LIST OF TRANSMISSION STRINGS
Symbols used in the strings
A = 1 byte for slave address (Example: Slave Nº 17: A = 0 x 11)
FUNCTION 1: READ COIL STATUS
QUERY
Address
Function 1
st
output address Nr of output
2 byte
Tot.byte
A
0x01
0x0000
0x0008
CRC
8
RESPONSE
Address
Function Nr of bytes Output status
2 byte
Tot.byte
A
0x01
0x01
0x00
CRC
6
Output status: 1 bit per output. 1st Output address = LSB of Output status. (1 = On, 0 = Off).
Status of outputs: In this byte each output is identified by 1 bit
The address of the 1st. output is the least significant bit (LSB) in this byte. (1 = On, 0 = Off).
