Today I'd like to share some knowledge about MODBUS communication, specifically how to monitor inverters or instruments directly using a touchscreen without going through a PLC. We'll use Siemens' SMART700IE touchscreen and Delta's VFD_M inverter as examples.
To achieve this kind of control, the following knowledge points need to be mastered:
1. Select the correct communication driver on the touchscreen:
Select the MidconMODBUS communication driver in the communication driver selection section, and set the corresponding parameters in the parameter settings section. These parameters must be consistent with the parameters set in the frequency converter (data bits, parity bits, stop bits, baud rate, station number, etc.).
II. Establishing variables in the touchscreen:
Establishing variable addresses is extremely important. We need to convert the addresses in the information frame into corresponding Modbus register information addresses (touchscreens only recognize Modbus register information addresses, not data addresses in the information frame, hence the need for conversion). To establish variable addresses, we need to understand the following:
(4) Correspondence between information frame data address and Modbus register address
MODBUS register address information can be divided into four types: 0XXX, 1XXXX, 3XXXX, and 4XXXX, depending on the function code. Therefore, we need to convert the address of the data frame into the corresponding Modbus register address. (Note: Different touchscreens may have more definitions for these addresses. For example, if the Vinylon touchscreen adds 5XXXX and 6XXXX types to the first definition of the Modbus address...)
For frequency inverters, if the read/write function of the frequency inverter is required, the main function codes used are 06 and 03 (Note: You can check the communication content in the frequency inverter manual to find the specific function codes used for read/write).
As shown in the diagram above, the starting address of the MODBUS register information address is 0001 (decimal) . The starting address of the information frame address is 0000H (hexadecimal), therefore we can obtain the following addresses:
Control command: 2000H corresponds to Modbus information address 48193 (4 indicates type: corresponding function code 03/06)
Frequency setting: 2001H corresponds to Modbus information address 48194
Read output frequency: 2103H corresponds to Modbus information address 48452
Read the output current: 2104H corresponds to Modbus information address 48453
Read the output voltage: 2106H corresponds to Modbus information address 48455
(5) Establish variable addresses in the touch screen
Establish the addresses of the remaining variables in the same way.
(to be continued)
