Latest revision as of 09:06, 6 May 2016

In this tutorial we are going to discuss the Timer module of LPC1768.
First we will see how to configure the Timer0 and Timer1 registers to generate delay of 100ms and 500ms respectively. At the end we will see how to use the ExploreEmdedded Timer library.

LPC1768 Timer Module

LPC1768 has four 32-bit independent timers (Timer0-Timer3). Each timer has a 32-bit pre-scalar to generate wide range on delays. Each timer has 4 match registers with which 4 different delays can be generated using a single timer.

LPC7168 Timer Registers

The below table shows the registers associated with LPC1768 Timer module.

Register	Description
IR	Interrupt Register: The IR can be read to identify which of 6(4-match, 2-Capture) 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-MR3	Match Registers: The Match register values are continuously compared to the Timer Counter value. When the two values are equal, actions can be triggered automatically. The action possibilities are to generate an interrupt, reset the Timer Counter, or stop the timer. Actions are controlled by the settings in the MCR register.

Register Configuration

TCR
31:2	1	0
Reserved	Counter Reset	Counter Enable

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

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

MCR
31:21	11	10	9	8	7	6	5	4	3	2	1	0
Reserved	MR3S	MR3R	MR3I	MR2S	MR2R	MR2I	MR1S	MR1R	MR1I	MR0S	MR0R	MR0I

MRxI
This bit is used to Enable or Disable the Timer interrupts when the TC matches MRx (x:0-3)
0- Disable the Timer Match interrupt
1- Enable the Timer Match interrupt.

MRxR
This bit is used to Reset TC whenever it Matches MRx(x:0-3)
0- Do not Clear.
1- Reset TC counter value whenever it matches MRx.

MRxS
This bit is used to Stop TC and PC whenever the TC matches MRx(x:0-3).
0- Disable the Timer stop on match feature
1- Enable the Timer Stop feature. This will stop the Timer whenever the TC reaches the Match register value.

Prescalar Calculation

Timer delay generated by the LPC1768 depends on the input clock and the pre-scalar values. The required pre-scalar value can be determined by the pclk (peripheral clock). PCLKSEL0 and PCLKSEL1 register have the PCLK info for all the 4 timers.

Timer	PCLKSELx	Bits	Symbol	Description
Timer0	PCLKSEL0	3-2	PCLK_TIMER0	Peripheral clock selection for TIMER0.
Timer1	PCLKSEL0	5-4	PCLK_TIMER1	Peripheral clock selection for TIMER1.
Timer2	PCLKSEL1	13-12	PCLK_TIMER2	Peripheral clock selection for TIMER2.
Timer3	PCLKSEL1	15-14	PCLK_TIMER3	Peripheral clock selection for TIMER3.

Getting the PCLK value.
Using the 2-bit information from PCLKSELx registers the pclk can be determined as below..

PCLKSELx bits	PCLK
0	SystemCoreClock/4
1	SystemCoreClock
2	SystemCoreClock/2
3	SystemCoreClock/8

Calculating the Pre-scalar value.
After getting the pclk value the prescalar count for 1us delay can be calculated as below.

Timer Working

Steps to Configure Timer

Power On the Timer module by setting the appropriate bits in PCONP register.
Configure MCR to reset the TC and generate the interrupt whenever it matches MRx.
Set the pre-scalar value for 1us.
Update the MRx register with required delay in micro secs.
Configure TCR to enable the Counter for incrementing the TC.
Enable the required timer interrupt.
Configure the GPIO pins as output for blinking the LEDs.
Toggle the LEDs in ISR whenever the interrupt is generated.

Example

Program to demonstrates the led blinking with 100ms and 500ms delay using the timer interrupts

Using ExploreEmbedded Libraries

In the above tutorial we just discussed how to configure and use the Timer module of LPC1768 to generate 100ms and 500ms delay
Once you know the internals of LPC7168 Timers, you can directly use the ExploreEmbedded libraries to generate the required Delays.
The below sample code shows how to use the ExploreEmbedded Timer library.

Timer Delay measured using CRO.

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!

@@ Line 1: / Line 1: @@
 [[category: LPC1768 Tutorials]]
-=Objective=
+In this tutorial we are going to discuss the Timer module of LPC1768.<br>
-In this tutorial we are going to discuss the TImer module of LPC1768.<br>
 First we will see how to configure the Timer0 and Timer1 registers to generate delay of 100ms and 500ms respectively. At the end we will see how to use the ExploreEmdedded Timer library.
 <br><br><br>
@@ Line 7: / Line 6: @@
 =LPC1768 Timer Module=
 LPC1768 has four 32-bit independent timers (Timer0-Timer3). Each timer has a 32-bit pre-scalar to generate wide range on delays.
-Each timer has 4 match registers with which 4 different delays can be generated using a single timer. Below table shows the registers associated with timers.
+Each timer has 4 match registers with which 4 different delays can be generated using a single timer.
+<br><br><br>
-{| class="table table-striped table-hover table-condensed table-bordered"
-|-class="info"
-!Adc 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
-|-class="active"
-|PWM_2|| P2.1  || 0-GPIO, 1-<b>PWM1[2]</b>, 2-RXD1, 3-             ||2,3 bits of PINSEL4    ||MR2
-|-
-|PWM_3|| P2.2  || 0-GPIO, 1-<b>PWM1[3]</b>, 2-CTS1, 3-TRACEDATA[3] ||4,5 bits of PINSEL4    ||MR3
-|-class="active"
-|PWM_4|| P2.3  || 0-GPIO, 1-<b>PWM1[4]</b>, 2-DCD1, 3-TRACEDATA[2] ||6,7 bits of PINSEL4    ||MR4
-|-
-|PWM_5|| P2.4  || 0-GPIO, 1-<b>PWM1[5]</b>, 2-DSR1, 3-TRACEDATA[1] ||8,9 bits of PINSEL4    ||MR5
-|-class="active"
-|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>
 =LPC7168 Timer Registers=
@@ Line 127: / Line 110: @@
 |-
 |3|| SystemCoreClock/8
-|}
+|}<br><br>
-=PWM Working=
+<b>Calculating the Pre-scalar value.</b><br>
-After looking into the PWM registers, its time to see how the LPC1768 PWM module works.
+After getting the pclk value the prescalar count for 1us delay can be calculated as below.
+<html>
+<script src="https://gist.github.com/SaheblalBagwan/53d0477123d605ea6819.js"></script>
+</html>
-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:
+=Timer Working=
-*Reset the TC value.
-*Pull the PWM pin High.
-*Loads the new Match register values.
-[[File:LPC1768_PWM.gif]]
 <br><br>
-Summary of PWM operations for the above image:
+=Steps to Configure Timer=
-*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.
+#Power On the Timer module by setting the appropriate bits in PCONP register.
-*Slide2: TC is incremented to 40 and still the PWM pin as HIGH.
+#Configure MCR to reset the TC and generate the interrupt whenever it matches MRx.
-*Slide3: TC is incremented to 60 and it matches the Duty Cycle(MR1=60).
+#Set the pre-scalar value for 1us.
-*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.
+#Update the MRx register with required delay in micro secs.
-*Slide5: TC is incremented to 80 and PWM pin is low as TC>Duty Cycle.
+#Configure TCR to enable the Counter for incrementing the TC.
-*Slide6: Now TC is 100 and it matches the Cycle time(MR0==100).
+#Enable the required timer interrupt.
-*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.
+#Configure the GPIO pins as output for blinking the LEDs.
-<br><br>
+#Toggle the LEDs in ISR whenever the interrupt is generated.
-=Steps to Configure PWM=
-#Configure the GPIO pins for PWM operation in respective PINSEL register.
-#Configure TCR to enable the Counter for incrementing the TC, and Enable the PWM block.
-#Set the required pre-scalar value in PR. In our case it will be zero.
-#Configure MCR to reset the TC whenever it matches MR0.
-#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).
-#Enable the bits in LER register to load and latch the new match values.
-#Enable the required pwm channels in PCR register.
 <br><br>
 =Example=
-Program to demonstrates the variable PWM signal generation on PWM_1-PWM_4(P2_0 - P2_3).<br>
+Program to demonstrates the led blinking with 100ms and 500ms delay using the timer interrupts<br>
-Connect the Leds to the pins P2_0 to P2_3 and observe the led brigthness change depending on the dutycycle.
-[[File:00_Lpc1768_Timer.jpg]]
 <html>
-<script src="https://gist.github.com/SaheblalBagwan/c721588560b77ad30396.js"></script>
+<script src="https://gist.github.com/SaheblalBagwan/2deb330218be6d06e694.js"></script>
 </html>
 <br><br><br>
-===Using ExploreEmbedded Libraries :===
+=Using ExploreEmbedded Libraries=
-In the above tutorial we just discussed how to configure and use the PWM module of LPC1768 <br>
+In the above tutorial we just discussed how to configure and use the Timer module of LPC1768 to generate 100ms and 500ms delay<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>
+Once you know the internals of  LPC7168 Timers, you can directly use the ExploreEmbedded libraries to generate the required Delays.<br>
-The below sample code shows how to use the ExploreEmbedded PWM library.<br>
+The below sample code shows how to use the ExploreEmbedded Timer library.<br>
 <html>
-<script src="https://gist.github.com/SaheblalBagwan/5df6b6cc86c3b9b546c2.js"></script>
+<script src="https://gist.github.com/SaheblalBagwan/598ef5205d03827d02f0.js"></script>
 </html>
+Timer Delay measured using CRO.
+[[File:Lpc1768 Timers.png]]
+<br><br>
+[[File:00_Lpc1768_Timer.jpg]]
 = Downloads=

Difference between revisions of "LPC1768: Timers"