Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module User Manual - Manual (Page 20)

Publication 1746-UM003A-EN-P
1-10 Overview
Module to Processor Communication
As shown in the following illustration, the RTD module communicates with
the SLC processor through the backplane of the chassis. The RTD module
transfers data to/receives data from the processor by means of an image table.
The image table consists of eight input words and eight output words when
configured for Class 1 operation; 16 input words and 24 output words when
configured for Class 3 operation. Data transmitted from the module to the
processor is called the input image (for example, Channel Data Words and
Channel Status Words). Conversely, data transmitted from the processor to the
module is called the output image (for example, Channel Configuration Words
and Scaling Limit Words). Details about the input and output images are
found in “Module Addressing” on page 3-2.
Figure 1.5 Communication Flow
The Channel Configuration Words (output image) contain user-defined
configuration information for the specified input channel. This information is
used by the module to configure and operate each channel. The Channel
Status Words (input image) contain status information about the channel’s
current configuration and operational state. The input data values of the
analog input channel are contained in the Channel Data Word (input image),
which is valid only when the channel is enabled and there are no channel errors
(for example, broken sensor or overrange.)
The user-set Scaling Limit Words (output image) provide a user-definable
scaling range for the temperature resistance data when using the proportional
counts data type.
Channel Data Words
Channel Status Words
Scaling Limit Words
Channel Configuration Words
1746-NR8
Input
Module
SLC 500
Processor
RTD/Resistance
Analog Signals
Chassis Backplane