I have recently bought an 8-channel Modbus data logger for reading 8 digital dial gauges from China. The equipment comes with a Modbus protocol documentation. However, I tried it using MBAXP Activex in Excel and also other Modbus testers and so far no luck to make a communication with the device. The document of the device can be found at the following link:
A picture of the equipment can be seen from:
I really appreciate it if anybody can assist me with this. Perhaps you will require more information on this and I will provide upon request.
As the data sheet is in Chinese but thanks to Google as language is not barrier. As per document page 7:-
Seven display box data output protocol
1. Data frame format:
MODBUS RTU mode
Communication parameters: baud rate 38400, 19200, 9600, 4800
Data frame: 1 start bit, 8 data bits, odd or even parity and no parity, 1 or 2 stop bits
Factory default value: baud rate 38400, 1 start bit, 8 data bits, no parity, 2 stop bits
MODBUS device address is 1
MODBUS data start address is 0, data is stored in addresses 0 and 1
Use MODBUS 0X03 to read commands
When reading with PLC, the data addresses are 40001 and 40002"
So the device support Modbus RTU with default factory settings of baud rate 38400, 1 start bit, 8 data bits, no parity, 2 stop bits MODBUS device address is 1.
The data is in Holding registers 40001 and 40002 so use function code of x03. If you are reading multiple meters by daisy chain then each meter should have unique Modbus device address. If 38400 baud rate is not working then set the meters to lower baud rate and test.