PWM

ECE 4437-EMBEDDED SYSTEMS

DR. GLOVER

CHRISTOPHER AHN & KHOA VAN

WHAT IS COVERED AND WHAT IS NOT• Cover:

• Count down mode and basic configuration to get the motor run.

• Not cover:

• Count up/down mode

• Dead band

• Interrupt

• Others

LOAD: Determines PWM period based on system clock

ADown/BDown: determine pulsewidthCOMPA/COMPB: we set the value to get Adown/BDown

ILLUSTRATION• Example: System clock is 80[Mhz] (can be reduced).

• PWM Clock will be:

• 80[Mhz]/64=1.25[Mhz] (period is 0.8 [us])

• We want:

• 2[ms] period. What is the Load value?

• Answer: LOAD= (2[ms]/0.8[us])-1

ILLUSTRATION• Now we need to generate pulse width,

• We will generate 20% duty cycle for PWMA for this example

• HOW?

• Easy: LOAD is 100%, so 20%*LOAD is the value for COMPA.

SUMMARY OF THE CODE:

• Initialize and enable the Clocks

• Enable the PWM Modules

• Configure Pin types

• Set Duty Cycle

• Enable the gate

• Enable generators

CODING EXAMPLE

Can be found on page 489 in:spmu298a_TivaWare_Peripheral_Driver_Lib.pdf