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2. Function descriptions of application layer
This section is aimed to define a general format of specific valid commands for KT system programmers. Each data query format
description is available, followed by explanations and examples of the function performed by the data query.
The protocol described in this section uses the format shown in Table 2.1 as much as possible (in hexadecimal numbers).
Device address
Function code
Variable start
address
High byte
Variable start
address
Low byte
Variable number
High byte
Variable number
Low byte
Check code
Low byte
Check code
High byte
03H
03H
00H
01H
00H
03H 55H
E9H
Table 2-1 Protocol example
2.1. Read data register (03H)
Function Code 03 enables users to obtain any data and system parameters collected and recorded by the device.
The following example is to read from Slave Device #3 three basic parameters collected – Phase A voltage, Phase B voltage and Phase
C voltage - (each address in the data frame occupies 2 bytes); and in the controller, Phase A voltage address is 01H, Phase B voltage
address 02H, and Phase C voltage address 03H.
Downstream message (from host to slave):
Device address
Function code
Variable start
address
High byte
Variable start
address
Low byte
Variable number
High byte
Variable number
Low byte
Check code
Low byte
Check code
High byte
03H
03H
00H
01H
00H
03H 55H
E9H
Table 2-2 Function Code 03 downstream message example
Upstream message (from slave to host):
The response includes the slave address, function code, number of data and CRC error check.
Device
address
Function
code
Variable
total byte
number
Variable
value
High byte
Variable
value
Low byte
Variable
value
High byte
Variable
value
Low byte
Variable
value
High byte
Variable
value
Low byte
Check code
Low byte
Check code
High byte
03H
03H
06H
00H
00H
00H
00H
00H
00H
38H
15H
Table 2-3 Function Code 03 upstream message example
2.2. Preset single register (06H)
Function Code 06 enables users to change the content in a single register. Any writable single register inside the controller can use this
function code to change its value. For example, preset the overload acting current register value as 03E0H and address as 2EH.
Downstream message (from host to slave):
Device address
Function code
Variable start
address
High byte
Variable start
address
Low byte
Variable value
High byte
Variable value
Low byte
Check code
Low byte
Check code
High byte
03H
06H
00H
2EH
03H
0E8H
E8H
9FH
Table 2-4 Function Code 06 downstream message example
A normal response to preset single register request is to transmit the received data back after the register value is changed.
Upstream message (from slave to host):
Device address
Function code
Variable start
address
High byte
Variable start
address
Low byte
Variable value
High byte
Variable value
Low byte
Check code
Low byte
Check code
High byte
03H
06H
00H
2EH
03H
0E8H
E8H
9FH
Table 2-5 Function Code 06 upstream message example
Instruction Leafl et
Effective September 2022
IZM6 Series Air Circuit Breaker
Operating Instruction Leafl et