PulseIn
Syntax
Assignment Variable = PulseIn Pin, State
Overview
Change the specified pin to input and measure an input pulse.
Parameters
Pin is a Port.Pin constant that specifies the I/O pin to use. State is a constant (0 or 1) or name High - Low that specifies which edge must occur before beginning the measurement. Assignment Variable is a user defined variable.
Example
Device = 24HJ128GP502 ' Select the device to compile for
Declare Xtal = 16
Declare Hserial_Baud = 9600 ' UART1 Baud rate
Declare Hrsout1_Pin = PORTB.14 ' Select pin is to be used for TX
Dim Var1 as Byte
RPOR7 = 3 ' Make PPS Pin RP14 U1TX
Do
Var1 = PulseIn PORTB.0, 1 ' Measure a pulse on pin 0 of PORTB.
HrsoutLn Dec Var1 ' Display the reading
DelayMs 500
Loop ' Repeat the processNotes.
PulseIn acts as a fast clock that is triggered by a change in state (0 or 1) on the specified pin. When the state on the pin changes to the state specified, the clock starts counting. When the state on the pin changes again, the clock stops. If the state of the pin doesn't change (even if it is already in the state specified in the PulseIn instruction), the clock won't trigger. PulseIn waits a maximum of 0.65535 seconds for a trigger, then returns with 0 in variable.
The variable can be either a Word or a Byte . If the variable is a word, the value returned by PulseIn can range from 1 to 65535 units.
The units are dependant on the frequency of the crystal used. If a 4MHz crystal is used, then each unit is 10us, while a 20MHz crystal produces a unit length of 2us.
If the variable is a byte and the crystal is 4MHz, the value returned can range from 1 to 255 units of 10µs. Internally, PulseIn always uses a 16-bit timer. When your program specifies a byte, PulseIn stores the lower 8 bits of the internal counter into it. Pulse widths longer than 2550µs will give false, low readings with a byte variable. For example, a 2560µs pulse returns a reading of 256 with a word variable and 0 with a byte variable.
