Data
A message sends data related to the function code.
The data transmission format differs depending on the function code.
Among the data used in Modbus communication, the 3G3M1 Series supports the following data types.
Data name Description
Coil Binary data (1 bit) that supports read/write operation
Holding register 16-bit data that supports read/write operation
Error Check
In Modbus communication, CRC (Cyclic Redundancy Check) is used for error checking.
The CRC code is 16-bit data generated for any data block with a data length in 8-bit units.
For CRC code generation, the following generator polynomial is used: CRC-16 (X
16
+ X
15
+ X
2
+ 1).
8-4-2
Required Communications Time
The time that the inverter takes to send a response after receiving a query is the sum of the silent in-
terval (3.5 characters) and the y19 (Communication Wait Time) set value.
After receiving a response from an inverter
, be sure to include an interval equivalent to the silent inter-
val (3.5 characters) or more before sending the next query to the inverter.
(Ex
am
ple
)
For 9,600 bps communications
One character: 10 bits (1 start bit + 8 data bits + 1 stop bit)
Time required per character: 1/9,600 (bps) × 10 (bit length) × 1,000 = 1.04 ms
Time required for 3.5 characters: 1.04 ms × 3.5 = 3.64 ms
However
, according to the Modbus specifications, this time is fixed to 1.75 ms for communications speeds
exceeding 19.2 kbps.
8-4-3
Normal Response
If the function code included in a query is for the Loop-back Test (08 hex), Write to Coil (05 hex, 0F
hex), or Write to Holding Register(s) (06 hex,10 hex) function, the inverter returns a response with the
same content as that of the query.
If the function code included in a query is for the Read Coil Status (01 hex) or Read from Holding Reg-
ister (03 hex) function, the inverter returns a response that includes data with the same slave address
and function code.
Refer to the later section,
8-5 Explanation of Each Function Code on page 8-11.
8-4-4
Abnormal Response
If an error (except for a communications error) is found in the query content, the inverter will return an
exception response without performing any operation. Refer to the later section, 8-5-9 Exception Re-
sponse on page 8-20.
Response
Slave address
8 Communications Functions
8-9
M1 Series Standard Type User's Manual (I669)
8-4 Modbus Communication Protocol
8
8-4-2 Required Communications Time
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