Demand Peripherals     Robotics and Automation Made Easy

PWMOUT4: Quad Pulse Width Modulated Output

PWMOUT4 gives you four channels of 12 bit PWM output. You can set the PWM counter to one of eight different frequencies. When used with the quad open-drain driver card the PWMOUT4 peripheral can control the speed of four DC motors or the brightness of four strings of LEDs.



The PWMOUT4 peripheral puts a PWM output on four FPGA pins. Each PWM output can be on from 0 to 4096 counts of the PWM clock. The outputs are not synchronized in any way. That is, one output might, or might not, start at the same time as another output. Typically, the outputs all start at different times but there is no guarantee of this. The PWM total period is always 4096 counts long.

PWMOUT4 works with any of the following cards:
     GPIO with pin headers
     GPIO with screw terminals
     Open-Drain Driver Card



pwm : PWM pulse widths as four hex numbers.
Specify the PWM duty cycles as hex numbers in the range of 0 to 1000. A value of 800 is fifty percent duty cycle. The maximum is 1000 (100% on) and the minimum is 0 (entirely off).
The pulse widths are separated by spaces and terminated by a newline. Each of the four pulse widths can vary between 000 and 1000.

config : clock rate in Hertz.
This is the frequency at which the PWM counter is incremented. Valid frequencies include: 20 MHz, 10 MHz, 2 MHz, 1 MHz, 500 KHz, 200 KHz, 100 KHz, and 0. A clock frequency of zero turns off all PWM outputs. The frequency of the PWM pulses is config frequency divided by 4096. This resource works with pcset and pcget.

The config frequency must be one of the following:
   2000000 -- 2 MHz
   1000000 -- 1 MHz
    500000 -- 500 KHz
    100000 -- 100 KHz
     50000 --  50 KHz
     10000 --  10 KHz
      5000 --   5 KHz
      1000 --   1 KHz
       500 -- 500 Hz
       100 -- 100 Hz
        50 --  50 Hz



Set the PWM counter frequency to 10 MHz. Set the PWM duty cycles to 25, 50, 75, and 100 percent. percent, and the two LSBs to 0 percent.

    # Set the PWM clock to 20 MHz
    pcset pwmout4 config 20000000
    # Set the PWM duty cycles to 25, 50, 75 and 100 percent
    pcset pwmout4 pwms 400 800 c00 1000