Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 146)

136 Timer/Counter Input Models
• A bit_count argument, which is the expected number of data bits to be
received and stored
• A max_period argument limiting the range of the timer/counter
measurement process
• A threshold argument, representing the half way point, in timer/counter
count clocks, between a zero data period and a one data period
The value returned by the io_in( ) function is the actual number of bits read. If
less than the expected number of bits (controlled by bit_count ) appear at the
input pin, the io_in( ) function waits for the max_period period before returning.
If the expected number of bits, or more, appear at the input pin, the io_in( )
function waits for silence at the input pin before returning. Silence is defined as
a lack of input cycles for the max_period period. If input cycles persist, the
function returns after 256 input cycles occur. This data may be retrieved using
the tst_bit( ) function.
The max_period argument is an unsigned long, and is passed as the negative
(two's complement) of the required value. The threshold argument is passed as
the max_period value plus the required threshold value. See Example on page
137. The edgelog input object type can be used to read inputs from infrared
devices that do not conform to the assumptions of the infrared input model.
Syntax
pin [input] infrared [mux | ded] [invert] [clock ( const-expr )] io-object-name ;
pin
An I/O pin. Infrared input can specify pins IO_4 through IO_7.
mux | ded
Specifies whether the I/O object is assigned to the multiplexed or dedicated
timer/counter. This field only applies, and must be used, when pin IO_4 is
the input pin.
The mux keyword assigns the I/O object to the multiplexed timer/counter.
The ded keyword assigns the I/O object to the dedicated timer/counter. The
multiplexed timer/counter is always used on pins IO_5 through IO_7.
invert
Causes the measurement of the cycle period to be between positive input
edges rather than the default, which is between negative input edges.
clock ( const-expr )
Specifies a clock in the range 0 to 7, where 0 is the fastest clock and 7 is the
slowest clock. The default clock for infrared input is clock 6. The
io_set_clock( ) function can be used to change the clock. Table 52 on page 137
shows the clock values for a Series 3100 device with an input clock of 10 MHz
and a Series 5000 device with a system clock of 80 MHz. The values in the
table can be adjusted for different input clocks by scaling them inversely
proportional to the change in input clock (for example, for a 20 MHz clock,
divide all values in the table by 2, and for a 5 MHz clock, multiply all values
in the table by 2).