HART Chips: Past, Present, Future
Revised
10-18-99
Revised 2-22-2000
Revised 3-12-2000
Analog Services, Inc. is proud to have participated in the design of several integrated circuits. Among them are the 20C12 Modem and the 20C15 Modem, both from Symbios (formerly NCR, then Symbios, now LSI Logic). The 20C12 was the first single-chip modem designed specifically for HART. It used a mere 400 uA of supply current and won major acceptance in the process control industry as the most practical way to incorporate HART into 2-wire process transmitters. The 20C12 was designed by Stephen Anderson of Analog Services, Inc. and Kathy Howard of Rosemount Inc.
The 20C12 has been discontinued, but has been cloned by Smar. The Smar version is the HT2012.
The 20C15 is a 20C12 with increased functionality. This was designed by Gabriel Maalouf of Rosemount Inc., David Tetzlaff of Rosemount Inc., and Stephen Anderson of Analog Services, Inc. Symbios was recently acquired by LSI Logic. There seems to be some question as to whether the 20C15 will survive. A spokesman for Rosemount Inc. says that they (Rosemount) have designed a new chip to replace the 20C15; and that it is pin-compatible with the 20C15. Again, this new chip will be available to HART designers through a major semiconductor vendor.
Schoppe & Faeser makes a HART Modem chip (no model number available) that is similar to the 20C15. That is, it has filters and waveshaping and on-board oscillator and consumes about 0.5 mA at 3 V.
The June, 1998 issue of Control Magazine estimated that there were about 5 million HART-compatible instruments in use. At about $4 to $5 per chip, this represents modem chip sales of 20 to 25 million dollars.
Because Bell-202 is still being used for Caller ID and other special telecom applications, other Bell-202 chips are also available. An example is the Silicon Systems 73K302. These were not designed for HART. They are not low-power and are somewhat cumbersome for use with HART. The Silicon Systems chip, for example, is intended to be connected to the micro-controller data bus and has several registers that must be written to configure and control it.
A recent article [Holland, S., "Low-Cost Software: Bell-202 Modem," Circuit Cellar, pp. 12-19, June, 1999] describes the implementation of a Bell-202 Modem entirely in the software of an embedded controller chip. The software is also apparently available for download from Circuit Cellar's web site. This software modem uses a very fast (50 MHz clock) microcontroller chip made by Scenix Semiconductor. The author says that there is still some processing power left over. We suspect that chips running much more slowly could also do the job.
Check out our VHDL HART modem (click here).
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E-Mail: stevea@analogservices.com