Allen-Bradley 1794-IT8, User Manual

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Overview of FLEX I/O and your Thermocouple/mV Module 1–2
Publication 1794-6.5.7
The adapter/power supply transfers data to the module (block
transfer write) and from the module (block transfer read) using BTW
and BTR instructions in your ladder diagram program. These
instructions let the adapter obtain input or output values and status
from the module, and let you establish the module’s mode of
operation. The illustration describes the communication process.
Typical Communication Between an Adapter and a Module
ADAPTER
ACTIVE FAULT
LOCAL
FAULT
24VDC
POWER SUPPLY
RIO ADAPTER
1794-ASB
Allen-Bradley
1
The adapter transfers your configuration data
to the module using a BTW.
Flexbus
External devices transmit
analog signals to the module.
2
The module converts analog signals
into binary format and stores these
values until the adapter requests
their transfer.
3
Your ladder program instructs the
adapter to perform a BTR of the values
and stores them in a data table.
4
The adapter and module determine
that the transfer was made without error and
input values are within specified range.
5
Your ladder program can use and/or move the data (if valid)
before it is written over by the transfer of new data in a
subsequent transfer.
6
Your ladder program performs BTWs to the module only when
you power it up, or any time you wish to reconfigure the module.
7
INPUT 0 INPUT 2 INPUT 4 INPUT 6 INPUT 1 INPUT 3 INPUT 5 INPUT 7
THERMOCOUPLE INPUT 8 CHANNEL
3
1794–IT8
Allen-Bradley
+ – + – + – + – + – +
–
+ – + –
OK