Difference between revisions of "LPC1768: PWM"

 
(38 intermediate revisions by the same user not shown)
Line 1: Line 1:
 
[[category: LPC1768 Tutorials]]
 
[[category: LPC1768 Tutorials]]
−
=Objective=
 
 
In this tutorial we are going to discuss the PWM module of LPC1768.<br>
 
In this tutorial we are going to discuss the PWM module of LPC1768.<br>
 
First we will see how to configure the PWM registers to generate signals of required PWM, At the end we will see how to use the ExploreEmdedded PWM  library.
 
First we will see how to configure the PWM registers to generate signals of required PWM, At the end we will see how to use the ExploreEmdedded PWM  library.
Line 10: Line 9:
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
|-class="info"
 
|-class="info"
−
!Adc Channel || Port Pin || Pin Functions || Associated PINSEL Register || Corresponding Match Register
+
!PWM Channel || Port Pin || Pin Functions || Associated PINSEL Register || Corresponding Match Register
 
|-
 
|-
 
|PWM_1|| P2.0  || 0-GPIO, 1-<b>PWM1[1]</b>, 2-TXD1, 3-            ||0,1 bits of PINSEL4    ||MR1
 
|PWM_1|| P2.0  || 0-GPIO, 1-<b>PWM1[1]</b>, 2-TXD1, 3-            ||0,1 bits of PINSEL4    ||MR1
Line 23: Line 22:
 
|-class="active"                                                                           
 
|-class="active"                                                                           
 
|PWM_6|| P2.5  || 0-GPIO, 1-<b>PWM1[6]</b>, 2-DTR1, 3-TRACEDATA[0] ||10,11 bits of PINSEL4  ||MR6
 
|PWM_6|| P2.5  || 0-GPIO, 1-<b>PWM1[6]</b>, 2-DTR1, 3-TRACEDATA[0] ||10,11 bits of PINSEL4  ||MR6
−
|}<br><br>
+
|}<br><br><br><br>
  
 
=LPC7168 PWM Registers=
 
=LPC7168 PWM Registers=
Line 66: Line 65:
  
 
'''Bit 0 – Counter Enable'''<br>
 
'''Bit 0 – Counter Enable'''<br>
−
This bit is used to Enable or Disable the PWM Timer and PWM Prescalar Counters
+
This bit is used to Enable or Disable the PWM Timer and PWM Prescalar Counters<br>
−
0- Disable the Counters
+
0- Disable the Counters<br>
 
1- Enable the Counter incrementing.
 
1- Enable the Counter incrementing.
  
 
'''Bit 1 – Counter reset'''<br>
 
'''Bit 1 – Counter reset'''<br>
−
This bit is used to clear the PWM Timer and PWM Prescalar Counter values.
+
This bit is used to clear the PWM Timer and PWM Prescalar Counter values.<br>
−
0- Do not Clear.
+
0- Do not Clear.<br>
 
1- The PWM Timer Counter and the PWM Prescale Counter are synchronously reset on the next positive edge of PCLK.
 
1- The PWM Timer Counter and the PWM Prescale Counter are synchronously reset on the next positive edge of PCLK.
 
    
 
    
 
'''Bit 3 – PWM Enable'''<br>   
 
'''Bit 3 – PWM Enable'''<br>   
−
Used to Eable or Disable the PWM Block.
+
Used to Enable or Disable the PWM Block.<br>
−
0- PWM Disabled
+
0- PWM Disabled<br>
 
1- PWM Enabled
 
1- PWM Enabled
 +
<br><br><br>
  
  
−
 
−
 
−
As all the LPC1768 SFRs(Special Function Registers) are defined in lpc17xx.h, this has to be included at the beginning of our project/code.
 
−
 
−
LPC1768 has its GPIOs divided into five ports PORT0 - PORT4, although many of them are not physically 32bit wide. Refer the data sheet for more info.
 
−
The Below registers will be used for Configuring and using the GPIOs registers for sending and receiving the Digital signals.
 
−
A structure LPC_GPIOn(n= 0,1,2,3) contains all the registers for required for GPIO operation. Refer lpc17xx.h file for more info on the registers.
 
−
 
−
<br><br>
 
−
 
−
<b>PINSEL:</b> GPIO Pins Select Register<br>
 
−
Almost all the LPC1768 pins are multiplexed to support more than 1 function. Every GPIO pin has a minimum of one function and max of four functions. The required function can be selected by configuring the PINSEL register. As there can be up to 4 functions associated with a GPIO pin, two bits for each pin are available to select the function. This implies that we need two PINSEL registers to configure a PORT pins.
 
−
By this the first 16(P0.0-P0.16) pin functions of PORT0 can be selected by 32 bits of PINSELO register. The remaining 16 bits(P0.16-P0.32) are configured using 32bits of PINSEL1 register. 
 
−
As mentioned earlier every pin has max of four functions. Below table shows how to select the function for a particular pin using two bits of the PINSEL register.
 
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
|-class="info"
 
|-class="info"
−
|Value||  Function || Enumeration
+
!MCR
 
|-
 
|-
−
|00|| Primary (default) function, typically GPIO port || PINSEL_FUNC_0
+
|31:21||20||19||18||-||5||4||3||2||1||0
−
|-
+
|-class="active"
−
|01|| First alternate function || PINSEL_FUNC_1
+
|Reserved||PWMMR6S||PWMMR6R||PWMMR6I||-||PWMMR1S||PWMMR1R||PWMMR1I||PWMMR0S||PWMMR0R||PWMMR0I
−
|-
+
−
|10|| Second alternate function || PINSEL_FUNC_2
+
−
|-
+
−
|11|| Third alternate function || PINSEL_FUNC_3
+
 
|}
 
|}
  
 +
'''PWMMRxI'''<br>
 +
This bit is used to Enable or Disable the PWM interrupts when the PWMTC matches PWMMRx (x:0-6)<br>
 +
0- Disable the PWM Match interrupt<br>
 +
1- Enable the PWM Match interrupt.
 +
 +
'''PWMMRxR'''<br>
 +
This bit is used to Reset PWMTC whenever it Matches PWMRx(x:0-6)<br>
 +
0- Do not Clear.<br>
 +
1- Reset the PWMTC counter value whenever it matches PWMRx.
 +
 
 +
'''PWMMRxS'''<br> 
 +
This bit is used to Stop the PWMTC,PWMPC whenever the PWMTC matches PWMMRx(x:0-6).<br>
 +
0- Disable the PWM stop o match feature<br>
 +
1- Enable the PWM Stop feature. This will stop the PWM whenever the PWMTC reaches the Match register value.
 +
<br><br><br>
  
  
−
<b>FIODIR:</b>Fast GPIO Direction Control Register.<br>This register individually controls the direction of each port pin.
 
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
|-class="info"
 
|-class="info"
−
|Values|| Direction
+
!PCR
 
|-
 
|-
−
|0|| Input
+
|31:15||     14-9    ||  8-7  ||        6-2        ||1-0
−
|-
+
|-class="active"
−
|1|| Output
+
|Unused||PWMENA6-PWMENA1||Unused||PWMSEL6-PWMSEL2||Unused
 
|}
 
|}
  
 +
'''PWMSELx'''<br>
 +
This bit is used to select the single edged and double edge mode form PWMx (x:2-6)<br>
 +
0- Single Edge mode for PWMx<br>
 +
1- Double Edge Mode for PWMx.
  
 +
'''PWMENAx'''<br>
 +
This bit is used to enable/disable the PWM output for PWMx(x:1-6)<br>
 +
0- PWMx Disable.<br>
 +
1- PWMx Enabled.
 +
<br><br><br>
  
−
<b>FIOSET:</b>Fast Port Output Set Register.<br>This register controls the state of output pins. Writing 1s produces highs at the corresponding port pins. Writing 0s has no effect. Reading this register returns the current contents of the port output register not the physical port value.
 
−
{| class="table table-striped table-hover table-condensed table-bordered"
 
−
|-class="info"
 
−
|Values||  FIOSET
 
−
|-
 
−
|0|| No Effect
 
−
|-
 
−
|1|| Sets High on Pin
 
−
|}
 
  
−
 
−
 
−
<b>FIOCLR:</b>Fast Port Output Clear Register.<br>This register controls the state of output pins. Writing 1s produces lows at the corresponding port pins. Writing 0s has no effect.
 
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
|-class="info"
 
|-class="info"
−
|Values||    FIOCLR
+
!LER
 
|-
 
|-
−
|0|| No Effect
+
|31-7||6||5||4||3||2||1||0
−
|-
+
|-class="active"
−
|1|| Sets Low on Pin
+
|Unused||LEN6||LEN5||LEN4||LEN3||LEN2||LEN1||LEN0
 
|}
 
|}
 +
'''LENx'''<br>
 +
This bit is used Enable/Disable the loading of new Match value whenever the PWMTC is reset(x:0-6)<br>
 +
PWMTC will be continously incrementing whenever it reaches the PWMMRO, timer will be reset depeding on PWMTCR configuraion.
 +
Once the Timer is reset the New Match values will be loaded from MR0-MR6 depending on bits set in this register.<br>
 +
0- Disable the loading of new Match Values<br>
 +
1- Load the new Match values from MRx when the timer is reset.
 +
<br><br><br><br><br>
  
 +
=PWM Working=
 +
After looking into the PWM registers, its time to see how the LPC1768 PWM module works.
  
 +
The TC is continuously incremented and once it matches the MR1(Duty Cycle) the PWM pin is pulled Low. TC still continues to increment and once it reaches the Cycle time(Ton+Toff) the PWM module does the following things:
 +
*Reset the TC value.
 +
*Pull the PWM pin High.
 +
*Loads the new Match register values.
  
 +
[[File:LPC1768_PWM.gif]]
 +
<br><br>
  
−
<b>FIOPIN:</b>Fast Port Pin Value Register.<br>This register is used for both reading and writing data from/to the PORT.<br>
+
Summary of PWM operations for the above image:
−
<b>Output:</b> Writing to this register places corresponding values in all bits of the particular PORT pins.<br>
+
*Slide1: The TC is being incremented as per the Pre-scalar configuration. The PWM output is high as the TC is still less that duty cycle.
−
<b>Input:</b>  The current state of digital port pins can be read from this register, regardless of pin direction or alternate function selection (as long as pins are not configured as an input to ADC).<br>
+
*Slide2: TC is incremented to 40 and still the PWM pin as HIGH.
−
<b>Note:</b>It is recommended to configure the PORT direction and pin function before using it.
+
*Slide3: TC is incremented to 60 and it matches the Duty Cycle(MR1=60).
−
<br><br><br><br>
+
*Slide4: Now the Comparator1(Green) will trigger the R of SR latch and Pulls the PWM output to Zero(Q=0). TC still continues to increment.
 +
*Slide5: TC is incremented to 80 and PWM pin is low as TC>Duty Cycle.
 +
*Slide6: Now TC is 100 and it matches the Cycle time(MR0==100).
 +
*Slide7: Now the Comparator2(Red) will trigger the S of SR latch and pulls the PWM output to ONE(Q==1). It also resets the TC to zero. It updates Shadow buffers with new Match values from MRO,MR1.
 +
<br><br>
  
−
=Examples=
+
=Steps to Configure PWM=
−
===Example 1===
+
#Configure the GPIO pins for PWM operation in respective PINSEL register.
−
Program to demonstrate the LED blinking.<br>
+
#Configure TCR to enable the Counter for incrementing the TC, and Enable the PWM block.
−
Here first the PORT2 pins are selected for GPIO using PINSEL register then they are configured as Output using the FIODIR register.<br>
+
#Set the required pre-scalar value in PR. In our case it will be zero.
−
LEDs are turned ON by sending a high pulse using FIOSET register.<br>
+
#Configure MCR to reset the TC whenever it matches MR0.
−
After some time the LEDs are turned OFF by sending the low pulse using FIOCLR register.
+
#Update the Cycle time in MR0. In our case it will be 100.
−
 
+
#Load the Duty cycles for required PWMx channels in respective match registers MRx(x: 1-6).
−
<html>
+
#Enable the bits in LER register to load and latch the new match values.
−
<script src="https://gist.github.com/SaheblalBagwan/17f76fb2a94206a9ee08.js"></script>
+
#Enable the required pwm channels in PCR register.
−
</html>
+
 
<br><br>
 
<br><br>
  
−
===Example 2===
+
=Example=
−
This is second approach in which FIOPIN register is used for both setting and clearing the PORT pins.<br>
+
Program to demonstrates the variable PWM signal generation on PWM_1-PWM_4(P2_0 - P2_3).<br>
−
Writing Logic 1 will set the PORT pin and writing 0 will Clear the particular PORT bit.
+
Connect the Leds to the pins P2_0 to P2_3 and observe the led brigthness change depending on the dutycycle.
−
 
+
[[File:0_LPC1768_PWM.gif]]
 
<html>
 
<html>
−
<script src="https://gist.github.com/SaheblalBagwan/f8d0d23dc5ad283f9e46.js"></script>
+
<script src="https://gist.github.com/SaheblalBagwan/c721588560b77ad30396.js"></script>
 
</html>
 
</html>
−
<br><br><br><br>
+
<br><br><br>
−
 
+
−
 
+
−
===Using Explore Embedded Libraries :===
+
−
In the above tutorial we just discussed how to configure the PORTS for GPIO for blinking the Leds.<br>
+
−
Once you know the GPIO configurations, you can directly use the ExploreEmbedded libraries to play around with LEDs.<br>
+
−
For that you need to include the gpio.c/gpio.h and the associated files(delay/stdutils).<br>
+
−
The below sample code shows how to use the GPIO functions.<br>
+
−
 
+
−
Refer this link for more info on GPIO libraries.
+
  
 +
===Using ExploreEmbedded Libraries :===
 +
In the above tutorial we just discussed how to configure and use the PWM module of LPC1768 <br>
 +
Once you know the internals of  LPC7168 PWM, you can directly use the ExploreEmbedded libraries to generate the required PWM signals for different duty cycles.<br>
 +
The below sample code shows how to use the ExploreEmbedded PWM library.<br>
 
<html>
 
<html>
−
<script src="https://gist.github.com/Amritach/5093f035b3b75909c255.js"></script>
+
<script src="https://gist.github.com/SaheblalBagwan/5df6b6cc86c3b9b546c2.js"></script>
 
</html>
 
</html>
−
 
−
[[File:0_LPC1768_PWM.gif]]
 
−
<br><br><br>
 
  
 
= Downloads=
 
= Downloads=

Latest revision as of 10:05, 8 May 2016

In this tutorial we are going to discuss the PWM module of LPC1768.
First we will see how to configure the PWM registers to generate signals of required PWM, At the end we will see how to use the ExploreEmdedded PWM library.


LPC1768 PWM Module

LPC1768 has 6 PWM output pins which can be used as 6-Single edged or 3-Double edged. There as seven match registers to support these 6 PWM output signals. Below block diagram shows the PWM pins and the associated Match(Duty Cycle) registers.

PWM Channel Port Pin Pin Functions Associated PINSEL Register Corresponding Match Register
PWM_1 P2.0 0-GPIO, 1-PWM1[1], 2-TXD1, 3- 0,1 bits of PINSEL4 MR1
PWM_2 P2.1 0-GPIO, 1-PWM1[2], 2-RXD1, 3- 2,3 bits of PINSEL4 MR2
PWM_3 P2.2 0-GPIO, 1-PWM1[3], 2-CTS1, 3-TRACEDATA[3] 4,5 bits of PINSEL4 MR3
PWM_4 P2.3 0-GPIO, 1-PWM1[4], 2-DCD1, 3-TRACEDATA[2] 6,7 bits of PINSEL4 MR4
PWM_5 P2.4 0-GPIO, 1-PWM1[5], 2-DSR1, 3-TRACEDATA[1] 8,9 bits of PINSEL4 MR5
PWM_6 P2.5 0-GPIO, 1-PWM1[6], 2-DTR1, 3-TRACEDATA[0] 10,11 bits of PINSEL4 MR6




LPC7168 PWM Registers

The below table shows the registers associated with LPC1768 PWM.

Register Description
IR Interrupt Register: The IR can be read to identify which of eight possible interrupt sources are pending. Writing Logic-1 will clear the corresponding interrupt.
TCR Timer Control Register: The TCR is used to control the Timer Counter functions(enable/disable/reset).
TC Timer Counter: The 32-bit TC is incremented every PR+1 cycles of PCLK. The TC is controlled through the TCR.
PR Prescalar Register: This is used to specify the Prescalar value for incrementing the TC.
PC Prescale Counter: The 32-bit PC is a counter which is incremented to the value stored in PR. When the value in PR is reached, the TC is incremented.
MCR Match Control Register: The MCR is used to control the reseting of TC and generating of interrupt whenever a Match occurs.
MR0 Match Register: This register hold the max cycle Time(Ton+Toff).
MR1-MR6 Match Registers: These registers holds the Match value(PWM Duty) for corresponding PWM channels(PWM1-PWM6).
PCR PWM Control Register: PWM Control Register. Enables PWM outputs and selects PWM channel types as either single edge or double edge controlled.
LER Load Enable Register: Enables use of new PWM values once the match occurs.






Register Configuration

The below table shows the registers associated with LPC1768 PWM.

TCR
31:4 3 2 1 0
Reserved PWM Enable Reserved Counter Reset Counter Enable

Bit 0 – Counter Enable
This bit is used to Enable or Disable the PWM Timer and PWM Prescalar Counters
0- Disable the Counters
1- Enable the Counter incrementing.

Bit 1 – Counter reset
This bit is used to clear the PWM Timer and PWM Prescalar Counter values.
0- Do not Clear.
1- The PWM Timer Counter and the PWM Prescale Counter are synchronously reset on the next positive edge of PCLK.

Bit 3 – PWM Enable
Used to Enable or Disable the PWM Block.
0- PWM Disabled
1- PWM Enabled



MCR
31:21 20 19 18 - 5 4 3 2 1 0
Reserved PWMMR6S PWMMR6R PWMMR6I - PWMMR1S PWMMR1R PWMMR1I PWMMR0S PWMMR0R PWMMR0I

PWMMRxI
This bit is used to Enable or Disable the PWM interrupts when the PWMTC matches PWMMRx (x:0-6)
0- Disable the PWM Match interrupt
1- Enable the PWM Match interrupt.

PWMMRxR
This bit is used to Reset PWMTC whenever it Matches PWMRx(x:0-6)
0- Do not Clear.
1- Reset the PWMTC counter value whenever it matches PWMRx.

PWMMRxS
This bit is used to Stop the PWMTC,PWMPC whenever the PWMTC matches PWMMRx(x:0-6).
0- Disable the PWM stop o match feature
1- Enable the PWM Stop feature. This will stop the PWM whenever the PWMTC reaches the Match register value.



PCR
31:15 14-9 8-7 6-2 1-0
Unused PWMENA6-PWMENA1 Unused PWMSEL6-PWMSEL2 Unused

PWMSELx
This bit is used to select the single edged and double edge mode form PWMx (x:2-6)
0- Single Edge mode for PWMx
1- Double Edge Mode for PWMx.

PWMENAx
This bit is used to enable/disable the PWM output for PWMx(x:1-6)
0- PWMx Disable.
1- PWMx Enabled.



LER
31-7 6 5 4 3 2 1 0
Unused LEN6 LEN5 LEN4 LEN3 LEN2 LEN1 LEN0

LENx
This bit is used Enable/Disable the loading of new Match value whenever the PWMTC is reset(x:0-6)
PWMTC will be continously incrementing whenever it reaches the PWMMRO, timer will be reset depeding on PWMTCR configuraion. Once the Timer is reset the New Match values will be loaded from MR0-MR6 depending on bits set in this register.
0- Disable the loading of new Match Values
1- Load the new Match values from MRx when the timer is reset.




PWM Working

After looking into the PWM registers, its time to see how the LPC1768 PWM module works.

The TC is continuously incremented and once it matches the MR1(Duty Cycle) the PWM pin is pulled Low. TC still continues to increment and once it reaches the Cycle time(Ton+Toff) the PWM module does the following things:

  • Reset the TC value.
  • Pull the PWM pin High.
  • Loads the new Match register values.

LPC1768 PWM.gif

Summary of PWM operations for the above image:

  • Slide1: The TC is being incremented as per the Pre-scalar configuration. The PWM output is high as the TC is still less that duty cycle.
  • Slide2: TC is incremented to 40 and still the PWM pin as HIGH.
  • Slide3: TC is incremented to 60 and it matches the Duty Cycle(MR1=60).
  • Slide4: Now the Comparator1(Green) will trigger the R of SR latch and Pulls the PWM output to Zero(Q=0). TC still continues to increment.
  • Slide5: TC is incremented to 80 and PWM pin is low as TC>Duty Cycle.
  • Slide6: Now TC is 100 and it matches the Cycle time(MR0==100).
  • Slide7: Now the Comparator2(Red) will trigger the S of SR latch and pulls the PWM output to ONE(Q==1). It also resets the TC to zero. It updates Shadow buffers with new Match values from MRO,MR1.



Steps to Configure PWM

  1. Configure the GPIO pins for PWM operation in respective PINSEL register.
  2. Configure TCR to enable the Counter for incrementing the TC, and Enable the PWM block.
  3. Set the required pre-scalar value in PR. In our case it will be zero.
  4. Configure MCR to reset the TC whenever it matches MR0.
  5. Update the Cycle time in MR0. In our case it will be 100.
  6. Load the Duty cycles for required PWMx channels in respective match registers MRx(x: 1-6).
  7. Enable the bits in LER register to load and latch the new match values.
  8. Enable the required pwm channels in PCR register.



Example

Program to demonstrates the variable PWM signal generation on PWM_1-PWM_4(P2_0 - P2_3).
Connect the Leds to the pins P2_0 to P2_3 and observe the led brigthness change depending on the dutycycle. 0 LPC1768 PWM.gif


Using ExploreEmbedded Libraries :

In the above tutorial we just discussed how to configure and use the PWM module of LPC1768
Once you know the internals of LPC7168 PWM, you can directly use the ExploreEmbedded libraries to generate the required PWM signals for different duty cycles.
The below sample code shows how to use the ExploreEmbedded PWM library.

Downloads

Download the complete project folder from the below link: https://codeload.github.com/ExploreEmbedded/Explore-Cortex-M3-LPC1768-Stick-DVB-14001/zip/master




Have a opinion, suggestion , question or feedback about the article let it out here!

Retrieved from "https://exploreembedded.com/wiki/index.php?title=LPC1768:_PWM&oldid=8927"