Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 134)

124 Timer/Counter Input Models
Introduction
A Neuron Chip or Smart Transceiver has two 16-bit timer/counters:
• For the first timer/counter, IO0 is used as the output, and a multiplexer
selects one of pins IO4 – IO7 as the input.
• The second timer/counter uses IO1 as the output and IO4 as the input.
Figure 46 shows the basic timer/counter circuits for the Neuron Chip and Smart
Transceiver.
Figure 46. Timer/Counter Circuits
A single application can declare multiple input devices that use timer/counter I/O
models. By calling the io_select() function, the application can use the first
timer/counter in up to four different input functions. If a timer/counter is
configured in one of the output functions, or as a quadrature input, then it cannot
be reassigned to another timer/counter object in the same application program.
The timing numbers shown in this chapter are valid for either an explicit I/O call
or an implicit I/O call through a when
clause, and are assumed to be for a Series
3100 Smart Transceiver running at 10 MHz.
Input timer/counter models have the advantage (over non-timer/counter objects)
in that input events are captured even if the application processor is occupied
doing something else when the event occurs. A when statement condition for an
event being measured by a timer/counter is TRUE when the measurement is
complete and a value is returned to an event register. If the processor is delayed
due to software processing and cannot read the register before another event
occurs, then the value in the register reflects the status of the last event. The
timer/counters are automatically reset upon completion of a measurement.
Timer/counter I/O models can also be used to trigger application-specific
interrupts. See the
Neuron C Programmer’s Guide for more information about
application interrupts.