Rockwell Automation 1770-HT8 SMART TRANSMITTER - Manual (Page 66)

Chapter
4
4-1
Communicating with the Smart Transmitter
Interface
This chapter provides programming information for communication
between host processors (programmable controllers and host computers)
and HART field devices via the Smart Transmitter Interface. It includes:
explanations of the data routing and protocol conversion functions of
the Smart Transmitter Interface
definitions of relevant communication terms
descriptions of HART and Smart Transmitter Interface data packets
a PLC-5 programming example that illustrates the use of these packets
for communicating between programmable controllers and HART field
devices
an explanation of serial communications with the Smart Transmitter
Interface
a brief note on using Data Highway Plus hosts with the Smart
Transmitter Interface
The Smart Transmitter Interface routes data packets between host
processors and HART field devices as illustrated in Figure 4.1.
Programmable controllers send and receive Smart Transmitter Interface
packets on the RIO link. Host computers send and receive DF1 packets on
the RS-232C link. The Smart Transmitter Interface converts the packets
from the host processor into packets conforming to the HART protocol (by
extracting the HART data and adding preambles) and relays them to the
specified HART field device. When it receives a packet from a HART field
device, the Smart Transmitter Interface converts it into the packet format
appropriate to the host processor and sends it on when required. The Smart
Transmitter Interface and HART field devices send and receive HART
packets over the 4-20 mA loops.
Data Routing and Protocol
Conversion