MODBUS communication in microcontroller based elevator controller

The elevator system uses microcontroller to perform real-time evaluation and analysis. The system includes huge number of switches and sensors which need to be connected to the microcontroller. The proposed method avoids the point-to-point connection of switches with the microcontroller by introducing independent hardware units to the each floor switches and car switches. These hardware units communicate to the main microcontroller through RS-485 Modbus network which requires only three wires. The control part of the protocol (address recognition, block integrity control and command interpretation) is implemented in software. The communication process is displayed on the HyperTerminal by connecting all units to the com port of PC using USB to serial converter and modeling sensors as toggle switches.