Inovance H3U Series - Page 616

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9 Communication 9.5.2 Setting the Modbus Conguration Table
As the baud rate of Modbus communication through the RS-485 interface is normally 9600 bps, the number
of "cyclic" items is limited to 10, and the number of "triggered" items per second is limited to 10. In this
case, data can be exchanged timely.
3) Suggestions for setting M variables
If you select the triggered mode, you need to enter the trigger condition in AutoShop. An M bit element can
be used as a trigger condition. When the bit element is set to ON, communication is triggered. Then the
system automatically clears the trigger ag. Therefore, the M ag can also be used to determine whether
communication is triggered. Therefore, when setting the communication conguration table, do not use
one M variable as the trigger ag for multiple communication operations; otherwise, other communication
operations may be triggered because the system clears the M ag.
4) Types of Modbus communication operations
In the
Function
column, you can enter types of operations: reading registers, writing registers, reading
coils, and writing coils. Registers are indicated by word variables (16-bit), and coils are indicated by bit
variables (1-bit variables, indicated by 0 or 1). You need to enter commands based on the type of variables.
a) Entering the slave register address
Before accessing internal variables of slaves, you need to understand rules for dening slave register
addresses. The following describes common address algorithms and precautions when PLCs, AC drives, or
servos serve as slave stations.
b) Register address of a slave PLC
It is the register address of a slave PLC when multiple PLCs are connected through Modbus protocols.
c) Address of a PLC register indicated by word variables
Word variables are 16-bit (word) or 32-bit (double-word) variables. D, T, and C0 to C199 are 16-bit
variables; C200 to C255 are 32-bit variables. The following table lists head addresses of registers (register
address = head address + variable number).
Variable Head Address
Number of
Registers
Description
D0 to D8511 0x0000 (0) 8512 16-bit register
SD0 to SD1023 0x2400 (9216) 1024 16-bit register
R0 to R32767 0x3000 (12288) 32768 16-bit register
T0 to T255 0xF000 (61440) 256 16-bit register
C0 to C199 0xF400 (62464) 200 16-bit register
C200 to C255 0xF700 (63232) 56 32-bit register
• Note: When the system accesses 32-bit registers of C200 to C255 through Modbus protocols, one register should
be regarded as two because the space occupied by a 32-bit register doubles that occupied by a 16-bit register.
For example, if registers of C205 to C208 will be read or written, the Modbus address is 0xF70A (0xF700 + 10),
and the number of registers is 8 (4 x 2).
d) Address of a PLC (register) indicated by bit variables
Bit variables of a PLC are also called "coils", for example, M, S, T, C, X, and Y variables, which are
indicated by 0 or 1. The following table lists head addresses of registers (register address = head address +
variable number).