Chip Design Principle of HART protocol (1)

We have already introduced many applications of the HART protocol. Here we mainly discuss another application of the HART protocol in the industry-the application design of the modem chip SYM20C15. In industrial control, the field instruments generally use 4 ~ 20mA standard. In order to expand the digitization function of existing instruments so that they can not only transmit measurement data, but also transmit diagnostic information, the existing four ~ 20mA increase the digital communication capability based on analog signals. Currently, the High Addressable Remote Transducer field communication protocol developed by Rosemount is widely used. SYM20C15 is a modem chip designed to implement the HART protocol.

1 HART communication protocol

The HART protocol uses the FSKFrequency Shift Keying Technology to convert digital signals into audio signals and overlay the four-to-four ~ 20mA current ring for digital communication. The signal frequency defined in the Protocol, namely, 1, 2, 202Hz, 0) and transmission rate, are in line with the US Bell standard. The average value of these audio sine waves is zero, so no DC components are added to the existing analog signals. Therefore, both analog and digital signals that do not affect each other can be transmitted at the same time on the two channels. It is precisely because of the advantages of the HART Protocol that it has become a widely used and de facto industrial standard in the industrial field.

2 SYM20C15 pin description and features

1) SYM20C15 pin description

SYM20C15 is a 28-pin PLCC package. Its pin description is shown in table 1.