ABB IMASI13, Инструкция по эксплуатации

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I/O Expander Bus
WBPEEUI240766B0 2 - 5
I/O Expander Bus Interface
The ASI module communicates with the controller through a
shared memory interface connected to the I/O expander bus.
The ASI module constantly updates the shared memory device
(dual port RAM) with the current values of the inputs. The con-
troller can read these values at any time, even if the ASI mod-
ule is simultaneously writing to the dual port RAM.
The ASI module uses a custom gate array for the I/O expander
bus interface. An integrated circuit holds all the control logic
and communication protocol. This integrated circuit provides
these functions:
•
Address comparison and detection.
•
Message decoding and translation.
•
Data line filtering of bus signals.
•
Onboard bus drivers.
•
Expander bus watchdog.
A dual port RAM stores data that can be accessed at the same
time by the controller and the I/O module's microcontroller.
Data Values
For all inputs, channel values are adjusted based on the fac-
tory calibration. Thermocouple inputs receive cold junction
reference compensation. Lead wire resistance adjustments are
performed when necessary (for cold junction reference only).
The ASI module provides values to the controller over the I/O
expander bus. These values are in engineering units.
The ASI module sends a status indication to the controller for
each input channel. This status indicates any hardware errors
and channel configuration errors detected by the ASI module.
Termination Units
The IMASI13 module uses one NTAI06 termination unit to
connect to field signals. An NKAS01 or NKAS11 cable connects
the termination unit to the ASI module through its P3 connec-
tor.
The termination unit contains RTDs used for cold junction
compensation of thermocouple inputs. They also contain the
circuitry needed to convert 4 to 20 milliampere field signals