IAI America ROBO Cylinder Series - Manual (Page 65)

5. Modbus RTU
57
Modbus
(4) Data
Use this field to add data specified by a function code. It is also allowed to omit data if data
addition is not specified by a function code.
(5) CRC check
In the RTU mode, an error check field confirming to the CRC method is automatically (Note)
included in order to check contents of all messages. Moreover, checking is carried out
regardless of the parity check method of individual characters in messages.
The CRC check consists of 16-bit binary values. The CRC value is calculated by the sender
that appends the CRC field to a message. The recipient recalculates the CRC value again
while receiving the message, and compares the calculation result against the actual value
received in the CRC field. If the two values do not match, an error will generate.
(Note) When using a PC or a PLC not supporting Modbus are used as the host, it is
necessary to create a function for calculating CRC.
Programs written in C language are included in 10, “CRC Check Calculation.”
Generation polynomial equation: x 16 + x15 + x2 + 1 (CRC-16 method)
(Reference) CRC calculation is automatically carried out with the FINS command supporting
Modbus RTU communication of the PLC CJ1 series made by Omron.
(6) End
This field contains a silent interval (non communication time) of 3.5 characters or longer.
(Note) If the response timeout error occurs, change parameter No. 45, “Silent interval
multiplier” or No. 17, “Min. delay for activating local transmitter” using the IAI’s
teaching tools as required.
(7) Broadcast
It is possible to send a query containing same data to all connected axes by specifying the
address 00
H
. In this case, no response is returned from an RC controller.
Note, however, that the function codes etc. that can be used with this function are limited; care
should be taken when using the function. Please check the function codes that can be used in 5.2,
“List of RTU Mode Queries.”
Fig. 5.1
PLC (master)
Address = 00
H
(command all axes)
RC controller
(slave)
RC controller
(slave)
RC controller
(slave)