Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 160)

150 Timer/Counter Input Models
Programming Considerations
A signed long value is returned from the io_in( ) function, based on the change
since the last input. The input is sampled every 50 ns for a Series 3100 device
with a 40 MHz input clock, or every 12.5 ns for a Series 5000 device with an 80
MHz system clock. This value scales inversely with the input clock speed.
For Series 3100 devices, add a #pragma enable_io_pullups directive to enable the
Neuron Chip's or Smart Transceiver's built-in pull-up resistors.
For more information on quadrature input, see the
Neuron Chip Quadrature
Input Function Interface engineering bulletin (part number 005-0003-01).
Syntax
pin [input] quadrature io-object-name ;
pin
An I/O pin. Quadrature input requires two adjacent pins. The pin
specification denotes the lower-numbered pin of the pair. The pin can be
IO_4 (which uses the dedicated timer/counter) or IO_6 (which uses the
multiplexed timer/counter).
Figure 56 shows the use of the two signal inputs A and B. Both edges of
input A are counted. Input B indicates whether input A is moving in a
positive or a negative direction.
io-object-name
A user-specified name for the I/O object, in the ANSI C format for variable
identifiers.
Figure 56. Quadrature Input
Usage
long input - value ;
input - value = io_in( io - object - name );