I/O System Diagnostic Data Collection - GE PACSystems RX7i Reference Manual

Chapter 4. CPU Operation

4.10.3 I/O System Diagnostic Data Collection

Diagnostic data in a PACSystems I/O system is obtained in either of the following two ways:
▪
If an I/O module has an associated bus controller, the bus controller provides the diagnostic data
from that module to the CPU. For details on GBC faults, see PACSystems Handling of GBC Faults.
▪
For I/O modules not interfaced through a bus controller, the CPU's I/O Scanner subsystem generates
the diagnostic bits based on data provided by the module.
The diagnostic bits are derived from the diagnostic data sent from the I/O modules to their I/O controllers
(CPU or bus controller). Diagnostic bits indicate the current fault status of the associated module. Bits
are set when faults occur and are cleared when faults are cleared.
Diagnostic data is not maintained for modules from other manufacturers. The application program must
use the BUS Read function blocks to access diagnostic information provided by those boards.
Note: At least two sweeps must occur to clear the diagnostic bits: one scan to send the %Q data
to the module and one scan to return the %I data to the CPU. Because module processing is
asynchronous to the controller sweep, more than two sweeps may be needed to clear the
bits, depending on the sweep rate and the point at which the data is made available to the
module.
Discrete I/O Diagnostic Information
The CPU maintains diagnostic information for each discrete I/O point. Two memory blocks are allocated
in application RAM for discrete diagnostic data, one for %I memory and one for %Q memory. One bit of
diagnostic memory is associated with each I/O point. This bit indicates the validity of the associated I/O
data. Each discrete point has a fault reference that can be interrogated using two special contacts: a fault
contact (-[F]-) and a no-fault contact (-[NF]-). The CPU collects this fault data if enabled to do so by the
programming software. The following table shows the state of the fault and no-fault contacts.
Condition
Fault Present
Fault Absent
Analog I/O Diagnostic Data
Diagnostic information is made available by the CPU for each analog channel associated with analog
modules and Genius analog blocks. One byte of diagnostic memory is allocated to each analog I/O
channel. Since each analog I/O channel uses two bytes of %AI and %AQ memory, the diagnostic memory
is half the size of the data memory.
The analog diagnostic data contains both diagnostics and process data with the process data being the
High Alarm and Low Alarm bits. The diagnostic data is referenced with the -[F]- and -[NF]- contacts. The
process bits are referenced with the high alarm (-[HA]- and low alarm (-[LA]-) contacts. The memory
allocation for analog diagnostic data is one byte per word of analog input and analog output allocated by
programming software. When an analog fault contact is referenced in the application program, the CPU
does an Inclusive OR on all bits in the diagnostic byte, except the process bits. The alarm contact is closed
if any diagnostic bit is ON and OFF only if all bits are OFF.
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[FAULT]
ON
OFF
PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual
[NOFLT]
OFF
ON
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