Mitsubishi Electric FR-E700 Instruction Manual page 488
Hide thumbs
Also See for FR-E700:
- Instruction manual (538 pages) ,
- Basic instruction manual (149 pages) ,
- Installation manuallines (38 pages)
Table of Contents
MODBUS®/TCP (FR-E700 SC ENE)
Message frame (protocol)
● Communication method
Basically, the master sends a query message (inquiry), and slaves return a response message
(response). At normal communication, the transaction identifier, protocol identifier, unit identifier,
and function code are copied as they are, and at erroneous communication (illegal function code
or data code), bit 7 (H80) of the function code is turned ON, and the error code is set at data bytes.
Fig. 6-173: Data interchange
Message frames comprise the six message fields shown in the figures above.
● Details of protocol
The following table explains the six message fields.
Transaction
identifier
2 x 8 Bit
Nachrichtenfeld
Transaction identifier
Protocol identifie
Length field
Unit identifier
Function code
Data
Tab. 6-122: Structure of the protocol
6 - 334
Query messages from master
Transaction identifier
Protocol identifier
Length field
Unit identifier
Function code
Eight-bit
Data bytes
Protocol
Length field
identifier
2 x 8 Bit
2 x 8 Bit
Beschreibung
The master adds the data for the purpose of transaction control.
The same data is returned in the response from the slave.
Fixed to 0. (When the slave receives data other than 0, it does not send the response message.)
0 is returned in the response from the slave.
The data length from the unit identifier to the data is stored in byte.
Fixed to 255
1 to 255 can be set in single byte length (8 bits) for the function code. The master sets the func-
tion to be sent to the slave as the request, and the slave performs the requested operation.
"Function code list" summarizes the supported function codes. An error response is generated
when a function code other than "Function code list" is set.
At a response from the slave, the function code set by the master is returned in the case of a
normal response. At an error response, H80 and the function code are returned.
The format changes according the function code. (Refer to page 6-336.) The data, for example,
includes the byte count, number of bytes, and accessing content of holding registers.
Transaction identifier
Protocol identifier
Length field
Unit identifier
Function code
Eight-bit
Data bytes
Response message from slave
Unit identifier
Function
8 Bit
8 Bit
Parameter
I001228E
Data
n x 8 Bit
- Quick Links:
- List of Alarm Display
Hide quick links:
Table of Contents
