First of all, give you the common communication methods in industry: 1, RS232 communication, also known as serial communication (more commonly used, older, slower transmission distance is generally not recommended for short distances greater than 10 meters, the highest communication speed of 1.2M / S but anti-jamming is not good), 2, RS485 communication (slow, but the distance is far away), 3, RS422 (and 485 is almost the same, but I Contact with the use of less) 4, Ethernet communication (fast speed can be up to 100M / S, there is no distance limit (because there is a network relay)) 5, USB (this thing is less in the industry, after all, anti-interference can not be, but the medical and household is more)
MODBUS is actually a public **** protocol is generally used in the serial communications, finished PLCs, screens, the devices more than 90% support the MODBUS protocol. devices more than 90% support MODBUS. But I said he is basically a serial port
And Siemens, Mitsubishi, even Panasonic, Omron 。。。。 These are just talking about PLC communication, just that each one has a format for each one, and according to this protocol (which is a format) to be able to read and write data, that's communication.