Modbus-Rtu Transmission Format; Read Command (03) - Toshiba Tosvert RS485 Instruction Manual

5.1. MODBUS-RTU transmission format

MODBUS-RTU sends and receives binary data without a frame-synchronizing start code and de-
fines the blank time to recognize the start of a frame. MODBUS-RTU decides the data that is first
received subsequently as the first byte of a frame after a blank time for 3.5 bytes at the on-going
communication speed.

5.1.1. Read command (03)

Computer → Inverter *The text size is 8 bytes fixed.
Inverter
(3.5bytes
No.
Blank)
1) Inverter No.. (1 byte)
2) Command (1 byte)
3) Communication No.. (2 bytes)
4) Number of data groups (2 bytes) : Set the number of data words 0001 (fixed) in the order of high to low numbers.
5) CRC (2 bytes)
Inverter → Computer (Normal return) *The text size is 7 bytes fixed.
Inverter
(3.5bytes
No.
Blank)
1) Command (1 byte)
2) Number of data
3) Read data (2 bytes)
Inverter → Computer (Abnormal return) *The text size is 5 bytes fixed.
(3.5bytes Inverter No. Command Error Code
Blank)
1) Command (1 byte)
2) Error code (1 byte)
Example: Reading output frequency (During 60Hz operation)
(Computer → inverter)
(Inverter → computer)
Example: Data specification error
(Computer → inverter)
(Inverter → computer)
Commu- Commu-
nication nication
Command
No.
(high) (low)
03
: Specify an inverter number between 0 and 247 (00H to F7H).
Command processing will be executed only broadcast communication "0" and with
those inverters that match set inverter numbers. Data will not be returned if "0"
(broadcast communication) and inverter numbers do not match.
: Set the read command (03H fixed).
: Set in the order of high to low numbers.
: Set generation results of CRC in the order of low to high numbers.. For the
method to generate CRC, see "5.2 CRC Generation." Note that the setting se-
quence is reversal to that of others.
Number of Read data
Command
Data
03 02
: Read command (03H fixed) will be returned.
: A number of data bytes (02H fixed) will be returned. The number of data groups for
transmission to the inverters is 2 bytes and 01H fixed. Note that the number of data re-
turned by the inverters is 1 byte and 02H fixed.
: Returned in the order of read data (high) and (low).
83
: 83H fixed (Read command error) (Command + 80H)
: See "4.3 Transmission errors."
01 03 FD 00 00 01 B5 A6
01 03 02 17 70 B6 50
01 03 FD 00 00 02 F5 A7
01 83 03 01 31
Number Number
of Data of Data
No. Groups Groups
(high) (low)
00 01
Read data CRC
(high) (low) (low)
CRC CRC
(low) (high)
30
E6581315
CRC CRC
(3.5bytes
(low) (high)
CRC
(3.5bytes
(high)
Blank)
(3.5bytes
Blank)
Blank)