User Manual

Chapter 7: Enabling and Using HART on the 1769sc-IF4IH0
U ser 's M a n u a l 0 300 21 5- 03 R ev. A
7-3
Figure 7-2
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Attention
Hart multi-drop is not supported by the IF4IH.
The HART module communicates to the controller using the input a nd output image.
Data communicated over the input and output image are transmitted at a rate that is
controlled by the PLC. The rate at which data is communicated to the controller and to
the compactbus is adjustable by using the RTS (Real Time Sample) and RPI (Requested
Packet Interval) respectively. The data passed via the input and output image include,
analog data, module status, HART data, and module specific commands.
Module specific commands include the HART pass-through commands, HART suspend,
HART resume, and the get HART device information command.
Gathering HART data is accomplished using two processes auto acquisition, and or
usin g the module specific commands.
7.2.2 Auto Acquisition
When a channel is configured for HART, the module will automatically search and
establish a connection to any HART field device wired to the channel. Once the module
establishes a connection it will begin to acquire HART data, including device specific
codes (i.e. Manufacturer ID, serial number, etc.), the four dynamic variables, extended
device status, slot variables (if enabled), and any stored ASCII message descriptor that
may be present. The HART data retrieved automatically by the module is then displayed
in the input image (If4ih0Input.HartData) and is accessible by ladder logic. The HART
data will update, on average, every 3.5 seconds if all four channels are enabled for
HART. The module initiates the connection by sending a string of HART commands to
the field device. Please see figure below.