The I/O Processor module provides the following functions:
ENCODER INPUT – Reads an absolute or AQUADB encoder; reports encoder
position and velocity to the PLC.
RANGE COMPARATORS – Updates 32 range comparators based on the latest
encoder reading and reports range comparator outputs to the PLC. The first 8 range
comparators also can control IOP digital outputs.
STROBE INPUTS – Up to four strobe input channels trigger the IOP to capture the
latest encoder readings and report them to the PLC.
STROBE TIMERS – Two input timers allow strobe pulse widths or time between
two different strobe channels to be measured and reported to the PLC.
The following sections explain these functions in more detail.
Encoder Input Function
The IOP module reads a parallel output Gray Code Encoder or an AQUADB Encoder
s. Encoder Gray Code data , Encoder Binary Code data, Encoder Total
Counts and Counts per Timebase (encoder velocity) are reported to the PLC on each I/O
scan using %AI data.
Absolute Gray Code Encoders must provide 256, 360, 512, or 1024 counts per revolution.
IOP Configuration allows the direction of encoder rotation to be electrically reversed.
IOP Configuration and %AQ immediate commands also allow a position offset to be
introduced. This offset value can eliminate the need to mechanically align the encoder
Absolute Encoders always use IOP inputs 1–8. Nine bit encoders require IOP input 9;
Ten bit encoders require IOP inputs 9 and 10.
AQUADB Encoders with an optional marker channel can also be used. The encoder
maximum (rollover) Binary Count value is configurable between 10 and 64999 counts.
Normally the maximum count value should be set to 1 less than the encoder counts per
revolution. However this is not a requirement and some applications may benefit from
the use of other rollover values.
Position initialization of AQUADB encoders can be accomplished in three ways:
1. The PLC can send a %AQ immediate command to initialize the encoder Binary
2. The PLC can initiate a Find Home operation which causes Binary Count data to be
set to the configured Home Position when the Home Switch input is ON and an
encoder marker rising edge transition occurs.
3. The encoder marker channel can be connected to the IOP faceplate Preload input. If
the %Q Reset Preload Latch bit is set ON, each marker rising edge transition will set
Encoder Binary Count data to the configured Preload value. This technique
provides a pseudo-absolute encoder function because Binary Count data is
re-initialized once per encoder revolution. For systems which can allow the encoder
to rotate at least one revolution before initializing position, operation will be similar
to an absolute encoder of equal resolution
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