ABSTRACT
It is an open process control hybrid communication network protocol that uses frequency shift keying (FSK) technique to superimpose digital communication signal on top of 4-20 mA current signal. The digital FSK signal has two frequencies 1200 and 2200 Hz, representing 1 and 0, respectively. It is backward compatible and operates in point-to-point or multidrop fashion.
Highway addressable remote transducer (HART) uses asynchronous mode for communication and length of HART character is 11 bits. It has two addressing modes: polling address and unique identifier—also known as short and long address.
Message transmission between master and slave takes place by arbitration. The master initiates message transmission in both master-slave or slave burst mode. For two masters, arbitration is based on timing.
A HART field device has a transducer block, a range block, and a data acquisition block by which the calibration of the device is done. HART protocol follows the seven layer open system interconnection (OSI) protocol but having only application, data link, and physical layers.
