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18.Annex 1
Modbus communication protocol
This protocol is based on the MODBUS-RTU protocol ("remote terminal unit" mode) to realize
remote control of hot water circulating pump equipment. The hot water circulating pump is
defined as a slave in the communication protocol.
18.1 UART configuration
18.1.1 One start bit, 8 data bits, low bit first
Start
Bit0
(low)
(LSB)
18.1.2 Baud rate: 115200bps
18.1.3 Check digit: None no check (factory default);
18.1.4 Stop bit: 1bit (default)
The communication configuration of the slave can be changed by the master after the
communication is established. Please refer to 18.5.2 corresponding register information.
18.2 Communication protocol
18.2.1 Adopt the master-slave mode, all communication must be initiated by the
master, and the slave should respond. Support single master-slave mode, the slave
address is fixed at 0x01.
18.2.2 Only the master has the right to initiate communication, and the slave only
responds after receiving legal and complete instructions from the master.
18.2.3 When the master sends data, it should be continuous, and there should be no
interval between each byte or the interval should be <1.5 byte time.
18.2.4 After the slave receives the command from the master, it starts to reply within at
least 50ms.
18.2.5 The slave should be continuous when sending data, and there should be no
interval between each byte or the interval should be <1.5 byte time.
18.2.6 After the master sends a frame of instructions, if there is no response, it will try
again every 200ms. If the communication cannot be carried out normally for a long
time, the host should deal with it accordingly.
18.2.7 If the slave machine does not receive a valid command for a long time, the slave
machine will also deal with it accordingly.
18.3 Protocol frame
Master to slave:
Address
Command
code
code
(8 bit)
(8 bit)
Slave to host:
Address
Command
code
code
(8 bit)
(8 bit)
Bit1
Bit2
Bit3
Data
CRCL
(N*8 bit)
(8 bit)
CRCL
Data
(8 bit)
(N*8 bit)
Bit4
Bit5
Bit6
CRCH
(8 bit)
CRCH
(8 bit)
157
Bit7
Parity
Stop
(high)
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