HCS12 Technical Training Module

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Version # : 1.0 Date: 04-April-2002

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HCS12 Technical TrainingModule

PWM

HCS12 Technical Training Module 9-PWM, Slide 2


What is PWM?

period

on

TT

Ratio Width Pulse

Ton Toff

Tperiod

Average

0 %

10 %

50 %

90 %

99 %

Applications: Digital-Analog Conversion Electrical Motor Control Tone Generation Sine Waveform Generation



Generation of PWM Signals (Edge Aligned)

Start

Period TPWM

TPWM

Duty Cycle TDuty

PWMDTYx PWMPERx PWMPERx

fClock, TClock

8-bit CounterPWMCNTx

Clock

8-bit Compare =PWMDTYx

8-bit Compare =PWMPERx

0x00 0x00

Reset

Pin



PWM Features

8 independent PWM channels with programmable period and duty cycle

Four clock sources with programmable clock select logic

Dedicated counter for each PWM channel

PWM duty pulse polarity for each channel

Enable/disable for each PWM channel

Double Buffering of period and duty cycle

Individual center aligned or left aligned outputs on each channel

Resolution: 8-bit (8 channel), 16-bit (4 channel)

Emergency shutdown with interrupt capability

Operation Modes



PWM Block Diagram

Channel 7

Period and Duty Counter

Channel 6


...Channel 0


Pin

Enable

Polarity

Alignment

Back

Pin

Pin



PWM Clock Select (1 of 4)1. Clock A (Ch 0, Ch 1, Ch 4, Ch 5)

2. Clock SA (scaled A; Ch 0, Ch 1, Ch 4, Ch 5)

3. Clock B (Ch 2, Ch 3, Ch 6, Ch 7)4. Clock SB (scaled B; Ch 2, Ch 3, Ch 6, Ch 7)

Four clock sources:

Bus ClockDivide by Prescaler Taps:

2 4 8 16 32 64 128

PRESCALE

PWMPRCLK @ $_03 Clock SA

Clock SB

Clock A

Further Division of the clock:

2 4 6 8 ... 512

Clock B

Further Division of the clock:

2 4 6 8 ... 512

PWMSCLA @ $_08

PWMSCLB @ $_09

SCALE



PWM Clock Select - PRESCALE (2 of 4)

0 PCKB2 PCKB1 PCKB0 0 PCKA2 PCKA1 PCKA0R

WReset: 0 0 0 0 0 0 0 0

= Unimplemented or Reserved

PWMPRCLK @ $_03

PCKx2 PCKx1 PCKx0 Value of Clock x

0 0 0 Bus Clock

0 0 1 Bus Clock / 2

0 1 0 Bus Clock / 4

0 1 1 Bus Clock / 8

1 0 0 Bus Clock / 16



1 1 1 Bus Clock / 128

Can be read and written anytime!x = A or B

Setting the PRESCALE Register:PWMPRCLK = 0x22; // B= Bus/4, A = Bus/4PWMPRCLK = 0x07; // B = Bus, A = Bus/128

Software Examples

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 0



PWM Clock Select - SCALE (3 of 4)

Bus ClockfBus

Divide by Prescaler Taps:

2 4 8 16 32 64 128

8-Bit Down Counter

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

PWMSCLxScale Value

SxClockxClockPWMSCLx

PWMSCLxxClockSxClock

_2_

2__

PWMSCLx = $00 PWMSCLx value is 256Can be read and written anytime!x = A or B

/ 2Clock Sx

Clock x

Clock x =fBus / PWMPRCLK

Count = 1

PWMPRCLK @ $_03

PWMSCLB @ $_09 PWMSCLA @ $_08

Example:Required: Clock Sx = 1 kHzBus Clock = 16 MHz

Prescaler = 128 Prescaler = 64Clock x = 125 kHz Clock x = 250 kHzPWMSCLx = 63 PWMSCLx = 125 Clock Sx = 992 Hz Clock Sx = 1000 Hz



PWM Clock Select (4 of 4)

PCLK6 PCLK5 PCLK4 PCLK3 PCLK2 PCLK1 PCLK0R

WReset: 0 0 0 0 0 0 0 0

PWMCLK @ $_02

PCLK7

PCLK7 — Pulse Width Channel 7 Clock Select1 = Clock SB is the clock source for PWM channel 7.0 = Clock B is the clock source for PWM channel 7.


PCLK5 — Pulse Width Channel 5 Clock Select1 = Clock SA is the clock source for PWM channel 5.0 = Clock A is the clock source for PWM channel 5.





PCLK0 — Pulse Width Channel 0 Clock Select1 = Clock SA is the clock source for PWM channel 0.0 = Clock A is the clock source for PWM channel 0.Back

Select Clock Source:PCLK0 = 1; // SA is source of ch 0PCLK6 = 0; // B is source of ch 6PWMCLK = 0x11; // all channels

Software Examples




PWMPERx

PWMDTYx

PWM Timer Channel

8-Bit Counter

PWMCNTx

8-Bit Compare =

PWMDTYx

8-Bit Compare =

PWMPERx

PWMCNT0 @ $_0CPWMCNT1 @ $_0DPWMCNT2 @ $_0EPWMCNT3 @ $_0FPWMCNT4 @ $_10PWMCNT5 @ $_11 PWMCNT6 @ $_12PWMCNT7 @ $_13

PWMDTY0 @ $_1CPWMDTY1 @ $_1DPWMDTY2 @ $_1E PWMDTY3 @ $_1FPWMDTY4 @ $_20 PWMDTY5 @ $_21PWMDTY6 @ $_22PWMDTY7 @ $_23

PWMPER0 @ $_14PWMPER1 @ $_15PWMPER2 @ $_16PWMPER3 @ $_17PWMPER4 @ $_18PWMPER5 @ $_19PWMPER6 @ $_1APWMPER7 @ $_1B

Polarity Bit = 1 Duty = High Time

Back

Channel xx = 0 ... 7

DoubleBuffered

DoubleBuffered

PWMDTYx

PWMPERx



Enable/Disable PWM

PWME6 PWME5 PWME4 PWME3 PWME2 PWME1 PWME0R

WReset: 0 0 0 0 0 0 0 0

PWME @ $_00

PWME7

Back

1 = Pulse Width channel x is enabled. The pulse modulated signal becomes available at PWM output bit x when its clock source begins its next cycle.

0 = Pulse Width channel x is disabled.

Channel 7 Channel 6 Channel 0...

Enable/Disable PWM channels:PWME5 = 1; // Enable PWM channel 5PWME3 = 0; // Disable PWM channel 3PWME = 0xFF // Enable all 8 PWM channelsPWME = 0; // Disable all 8 PWM channels

Software Examples




PWM Polarity Enable Register

PPOL6 PPOL5 PPOL4 PPOL3 PPOL2 PPOL1 PPOL0R

WReset: 0 0 0 0 0 0 0 0

PWME @ $_00

PPOL7


1 = PWM channel x output is high at the beginning of the period, then goes low when the duty count is reached.

0 = PWM channel x output is low at the beginning of the period, then goes high when the duty count is reached.

Back

PWMDTYx

PWMPERx

PPOLx = 1

PWMDTYx

PWMPERx

PPOLx = 0




Left Aligned Output (1 of 3)

Clock SourceE = 100 ns

Duty Cycle= 75 %

Period= 400 ns

%100_:1

%100_:0

),,,(_

PWMPERxPWMDTYxCycleDutyPolarity

PWMPERxPWMDTYxPWMPERxCycleDutyPolarity

PWMPERxSBSABAClockFrequencyPWMx

Clock Source = E = 10 MHz (100 ns period)PPOLx = 0PWMPERx = 4PWMDTYx = 1

PWMx Frequency = 10 MHz/4 = 2.5 MHzPWMx Period = 400 nsPWMx Duty Cycle = ¾*100% = 75%

Start



Center Aligned Output (2 of 3)

PWMDTYxE = 100ns

Period = PWMPERx*2= 800 ns

%100_:1

%100_:0

2),,,(_

PWMPERxPWMDTYx

CycleDutyPolarity

PWMPERxPWMDTYxPWMPERxCycleDutyPolarity

PWMPERxSBSABAClockFrequencyPWMx

Clock Source = E = 10 MHz (100 ns period)PPOLx = 0PWMPERx = 4PWMDTYx = 1

PWMx Frequency = 10 MHz/8 = 1.25 MHzPWMx Period = 800 nsPWMx Duty Cycle = ¾*100% = 75%

Start

PWMDTYxE = 100ns

PWMPERx PWMPERx

Duty Cycle = 75%



PWM Center Align Enable Register (3 of 3)

Back

CAE6 CAE5 CAE4 CAE3 CAE2 CAE1 CAE0R

WReset: 0 0 0 0 0 0 0 0

PWMCAE @ $_04

CAE7


CAEx – Center aligned Output Mode on channel x1 = Channel x operates in Center Aligned Output Mode0 = Channel x operates in Left Aligned Output Mode




16-Bit ResolutionTwo 8-bit channels of the PWM module can be concatenated to a 16-Bit PWM channel

Period/Duty Compare

PWMCNT6 PWMCNT7

PWM7

Clock Source 7

CONxx PWMEx PPOLx PCLKx CAEx PWMx OUTPUT

CON67 PWME7 PPOL7 PCLK7 CAE7 PWM7



CON01 PWME1 PPOL1 PCLK1 CAE1 PWM1Back



Emergency Shutdown

Emergency ShutdownChannel 7

Channel 6


Channel 5


...Channel 0


FaultInput PWMLVL=1 PWMLVL=0

PWM7INL=1

PWMLVL=0

InterruptPWMIE

PWMIF



PWM Shutdown Register

PWMIE PWMRSTRT

PWMLVL 0PWM7INL PWM7EN

R

WReset: 0 0 0 0 0 0 0 0

PWMSDN @ $_24

PWMIF

Back

0 PWM7IN


Set shutdown active levelPWM7INL

Set shutdown output levelPWMLVL

Enable emergency shutdownPWM7ENA

Initialisation

Interrupt EnablePWMIE




Modes of Operation

Wait Mode

Allow input clock to prescaler

while in WAIT

PSWAI=

10

Stop input clock to prescaler

while in WAIT

Freeze Mode

PWM continue while in FREEZE

PFRZ=

10

Disable input clock to prescaler

while in FREEZE



PWM Control Register

CON45 CON01 0PSWAIR

WReset: 0 0 0 0 0 0 0 0

PWMCTL @ $_05

CON67


CON23 PFRZ 0Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 0

16 bit operation

Enable/Disable clockin WAIT

Enable/Disable clockIn FREEZE

Back



PWM Channel Period Registers

Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0R

WReset: 1 1 1 1 1 1 1 1

PWMPERx @ $_14-_1B

Bit 7

Back

PeriodClockChannelPeriodPWMxPWMPERx

PWMPERxPeriodClockChannelPeriodPWMx

__2_

2___0)(CAExOutput AlignedLeft

OutputAlignedCenterPeriodPWMxPWMPERx

OutputAlignedCenterPWMPERxPeriodClockChannelPeriodPWMx

__2_

_____1)(CAExOutput AlignedCenter




PWM Channel Duty Registers

Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0R

WReset: 1 1 1 1 1 1 1 1

PWMDTYx @ $_1C-_23

Bit 7

Back

%100_

1)(PPOLx 1 Polarity

%100_

0)(PPOLx 0 Polarity

PWMPERxPWMDTYxCycleDuty

PWMPERxPWMDTYxPWMPERxCycleDuty




Setup the PWM

1. Disable PWMPWME

2. Select clock (prescaler and scale) for the PWM PWMPRCLK, PWMSCLA, PWMSCLB, PWMCLK

3. Select polarityPWMPOL

4. Select center or left aligned modePWMCAE

5. Program duty cycle and periodPWMDTYx, PWMPERx

6. Enable used PWM channelsPWME

HCS12 Technical Training Module

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