PWM Output

Programs the PWM outputs of the Q8 data acquisition system.

Library

qctools

Description

The PWM Output Module for the Q8 series of I/O cards programs one of the 32-bit general purpose counters to output a PWM signal on an external pin. The polarity of the CNTR_EN input may also be configured for hardware enabling/disabling of the counter. The CNTR_EN line only affects the COUNTER clock source. Unlike the Counter Output block, the PWM Output block reprograms the duty cycle every sampling instant, according to its input. Note that when the current duty cycle is non-zero, the new duty cycle is activated at the end of the next PWM period. Hence there are no spurious output values during transitions.

Block Inputs

Duty Cycle

The duty cycle is a scalar fraction ranging from 0 to 1. A value of 0 represents a duty cycle of 0% (output always low) and a value of 1 represents a duty cycle of 100% (output always high). A value less than 0 will be treated as 0. A value greater than 1 will be treated as 1.

Parameters and Dialog Box

Board Number

The board number of the I/O card. If there is only one Q8 board in your system, then the board number should be zero. The second Q8 board in your system is board number 1, etc.

Clock Source

The clock source to use as the counter. If COUNTER is selected, then the PWM signal will appear on the CNTR_OUT pin of the CONTROL header on the terminal board. If WATCHDOG is selected, then the PWM signal will appear on the WATCHDOG pin of the CONTROL header on the terminal board.

Period

The period in seconds of the output signal. The period may range from 60 ns to 257 seconds (4.3 minutes), in 60 ns units.

Sample Time

The sample time for the block. Each sampling instant, the block reads its input and sets the duty cycle of the PWM signal accordingly. The duty cycle changes when the PWM period expires (except when the duty cycle is 0% or 100%) so that there are no spurious output values.

CNTR_EN Polarity

Polarity of the CNTR_EN input. If this option is not checked then the CNTR_EN is an active-low input. Otherwise it is active-high. The CNTR_EN line has a pullup resistor to bring it high when the input is unconnected. Hence, this option is normally checked to enable the counter by default.