Rockwell Automation 1770,D17706.5.21 SMART TRANSMITTER TOOLKI - Manual (Page 11)

Chapter 1
Introducing The Smart Transmitter Toolkit
1-4
To help explain what the STT subroutine can do for you, let’s examine how
communication occurs between a PLC processor and a HART field device.
➊
The PLC-5 processor sends a Smart Transmitter Interface packet to
the 1770-HT1 as block-transfer write (BTW) data.
➋
The 1770-HT1 forwards the Smart Transmitter Interface packet as a
HART packet to the HART field device.
❸
The HART field device receives the HART packet and then responds
back to the 1770-HT1 with a HART packet that contains the
appropriate HART digital data.
➍
The 1770-HT1 routes the response back to the PLC-5 processor in a
Smart Transmitter Interface packet as block-transfer read (BTR) data.
90065
HART Response
HART
Field
Device
BTW Data
RIO
BTR Data
HART Poll
4Ć20 mA Loop
1770ĆHT1
Smart Transmitter
Interface packet
➊
❸
➋
➍
HART
packet
1770ĆHT16
Smart Transmitter Interface
PLCĆ5 Processor
How a PLCĆ5 Processor
Communicates With a HART
Field Device