Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 32)

22 Introduction
}
}
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I/O Events
An alternative to using the explicit io_in( ) function is to associate an input object
with a predefined event or interrupt. The two I/O-related predefined events are:
• io_changes
• io_update_occurs
These events are used only with input objects. When they are evaluated, both
the io_update_occurs and io_changes events perform an implicit io_in( ) function
call to obtain an input value for the object. Your program can access this input
value by using the input_value variable.
You can also associate timer/counter I/O devices or individual I/O pins with
application interrupts on a Series 5000 device. See the
Neuron C Programmer’s
Guide for more information about application interrupts.
io_changes Event
This event is TRUE when the value read from the specified input object changes
state. The change can be one of three types:
• Any change (an unqualified change)
• A change (in absolute value) by a specified amount (or greater)
• A change to a specified value
The syntax for this event is:
io_changes( io-object-name ) [by expr | to expr ]
The use of this event results in a comparison of the current value read from the
input object with a reference value (except for the to option). The reference value
is the value that was read the last time the change event evaluated to TRUE
(and saved, at that time, by the firmware). For an io_changes event that does not
use either the by option or the to option, a state change occurs when the current
value is different from the reference value. When using the optional forms of the
io_changes event, the expr expression does not need to be a constant. However, a
constant expression is more efficient.
The io_changes event for a timer/counter input device occurs only if the device
has a new value, different from the previous value. For the timer/counter devices,
the io_changes event happens as listed in Table 8, depending on the input object
type.
Table 8. io_changes Events for Specific I/O Models
I/O Model Event
dualslope Event occurs when the conversion is complete.