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This bit is used Enable/Disable the loading of new Match value whenever the PWMTC is reset(x:0-6)<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.
 
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.  
+
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>
 
0- Disable the loading of new Match Values<br>
 
1- Load the new Match values from MRx when the timer is reset.
 
1- Load the new Match values from MRx when the timer is reset.

Revision as of 15:54, 24 March 2016

Objective

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.

Adc 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.

Examples

Example 1

Program to demonstrate the LED blinking.
Here first the PORT2 pins are selected for GPIO using PINSEL register then they are configured as Output using the FIODIR register.
LEDs are turned ON by sending a high pulse using FIOSET register.
After some time the LEDs are turned OFF by sending the low pulse using FIOCLR register.



Example 2

This is second approach in which FIOPIN register is used for both setting and clearing the PORT pins.
Writing Logic 1 will set the PORT pin and writing 0 will Clear the particular PORT bit.






Using Explore Embedded Libraries :

In the above tutorial we just discussed how to configure the PORTS for GPIO for blinking the Leds.
Once you know the GPIO configurations, you can directly use the ExploreEmbedded libraries to play around with LEDs.
For that you need to include the gpio.c/gpio.h and the associated files(delay/stdutils).
The below sample code shows how to use the GPIO functions.

Refer this link for more info on GPIO libraries.

0 LPC1768 PWM.gif


Downloads

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




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