Timer_S05

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Timers

ME4447

INTRODUCTION TO MECHATRONICS

Anthony Wingo

Carlos Alzate

Jim Kitchen

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A look at how the timer has evolved.

Provides earliest evidence of day and night seperation

Had to be made for specific latitudes

Sundial from about 16th century B.C.

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The sundial works fine, if it is used on an unclouded day.

A look at how the timer

has evolved.

Sundial from about 16th century B.C.

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Astrolabe from about 2nd century A.D.

Has ability to find and measure time

Based on map constructed by Hipparchus around 150 B.C.

Helped in construction of sundials.

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Candle Clock from about 9th century A.D.

Inserting a nail at a pre-determined location,the candle clock could be used as a timer.

Imagine interfacing this idea with the HC11.

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Hour Glass came probably from Europe before the 14th century.

The medium flowed from one end through a passage that is

10 times larger than the medium particles.

Sailors used the hour glass to calculate speed at sea.

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Weight driven clock from 1270s and probably Europe.

Time of invention as well as inventor is still unknown.

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Spring driven clock from around 15th century A.D.

Bringing the tower clocks into homes.

Prone to inaccuracy due to the mainspring

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Pendulum Clock by Christiaan Huygens in 1656

First clock to count seconds.

Galileo started the idea but died before implementing it.

Accuracy was increased to a loss of only a few seconds per day.

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Cesium atomic clock

Britain's National Lab 1955

Most accurate of any time-keeping device described.

Not very portable or cost efficient in small projects

Accuracy of 2 nanoseconds/day or 1 second per 1,400,000 years.

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555 Timer

• What is the 555 Timer

• 555 schematic• Pin Configurations

• Monostable Mode

• Astable Mode

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What is the 555 Timer?

• Integrated Circuit

• Transistors, Diodes, Resistors

• Designed and invented in 1970 by HansR. Camezind

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Pin Configurations

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Monostable Mode

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Monostable Output Voltage

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Monostable Characteristics

• Generates a single pulse of a fixed timeduration each time it receives an inputtrigger pulse

• Length of pulse depends on when thecapacitor reaches 66.6% V

• Length of pulse is given by:

C Rt p 1.1

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Monostable Applications

• Turning a circuit or external componenton / off for a specific length of time

• Generate delays

• Multiple pulses can be used to time andsequence other related applications

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Astable Mode

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Astable Output Voltage

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Animation

http://www.williamson-labs.com/480_555.htm





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Astable Characteristics

• Outputs continuous stream of pulses• Triggers from previous output pulse

• Frequency of series of pulses

2

21

693.0

693.0

1

highstays pinoutputheduration t

RC t

R RC t

t t f

l

h

l h

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Astable Applications

• Create an accurate clock signal

• Modulate transmitters such as ultrasonicand IR transmitters

• Turn on / off actuator at set intervals for afixed duration

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HC11 Timer Functions

Fast Fact:Of 64 Register on the HC11,

29 are used for timing functions

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HC11 Timer Functions

• Port A• Main Timer

• Measuring Long Times – Prescaler

– 24-bit time

• Inputs – Input Capture

– Pulse Accumulator

• Outputs – Output Compare

– Real Time Interrupts

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Port A

PA7 PA6 PA5 PA4 PA3 PA2 PA1 PA0Port A $1000

OC1 OC1 OC1 OC1 OC1

PAI OC2 OC3 OC4OC5/IC4 IC1 IC2 IC3

DDRA7 PAEN RTR0PACTL $1026PAMOD PEDGE DDRA3 I4/O5 RTR1

01234567

•PA7 direction is changed by setting DDRA7

•PA3 direction and function is changed by setting DDRA3 and I4/O5

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Main Timer

• The HC11 Timer is a 16-bit read-only register

• Rolls over (overflows) from $FFFF to $0000

every 0.5μs*216

= 32.768ms

Bit 15 - Bit 8

Bit 7 Bit 0TCNT $100F

$100E- - - - -

- - - - - -

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Main Timer

• When the main timer overflows, the TOF flag isset

• If the TOI bit is set, an overflow will alsogenerate an interrupt

TOF RTIF 0TFLG2 $1025PAOVF PAIF 0 0 0

01234567

TOI RTII PR0TMSK2 $1024PAOVI PAII 0 0 PR1

01234567

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Measuring Long Times: Prescaler

• The prescaler will slow down theincrements of the main timer, allowing forrecording of longer time intervals

• E-Clock rate is divided by: 1, 4, 8, or 16 – Default prescale factor is 1

– Must be set during the first 64 E-Clock cyclesafter reset

• Trade-off between resolution and timebetween overflows

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Measuring Long Times: Prescaler

TOI RTII PR0TMSK2 $1024PAOVI PAII 0 0 PR1

01234567

PrescaleFactor

E Clock = 2MHz

PR1 PR0Resolution

(one count)

Range

(Overflow)

Frequency

(Overflow)

1

4

8

16

0.5 ms

2.0 ms

4.0 ms

8.0 ms

32.77 ms

131.1 ms

262.1 ms

524.3 ms

30.5 Hz

7.63 Hz

3.82 Hz

1.91 Hz

0

0

1

1

0

1

0

1

•Prescaler is set with bits PR1 and PR0

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Measuring Long Times: 24-bit time

• 24-bit time can be used to extend therange of the timer

• Accomplished by storing the # of overflowsthat have occurred in a memory location

• Store and compare 24-bit times: increasesthe range from 32.8 ms to 8.4 s

• Better resolution than prescaler, butharder to implement

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Important Note

• In almost all timer functions, severalcommon things happen

– A flag is set (must be cleared by user)

– An interrupt can be generated (optional)

– An event happens, dependent on the functionbeing used

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Inputs: Input Capture

• Used to record the clock time when an edge is detectedon one of the input pins

• The time is stored in a register (read-only) by storing thecontents of the free-running counter in the input captureregisters (16-bits)

Bit 15 - Bit 8

Bit 7 Bit 0

TIC1$1011

$1010

Bit 15 Bit 8

Bit 7 Bit 0

TIC2$1013$1012

Bit 15 Bit 8

Bit 7 Bit 0

TIC3

$1015

$1014

- - - - -

- -- - - -

- - - - - -

- -- - - -

- - - - - -

- -- - - -

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Configuration EDGxB EDGxA

Capture Disabled 0 0Capture on Rising Edge Only 0 1

Capture on Falling Edge Only 1 0

Capture on Any Edge 1 1

EDG3ATCTL2 $1021

01234567

EDG3BEDG2AEDG2BEDG1AEDG1BEDG4AEDG4B

• Which edge to capture on can be configured withthe TCTL2 register

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• Flags are set when a capture is made

• Interrupts can be generated if the mask bits are

set

OC1F OC2F IC3F

TFLG1 $1023OC3F OC4F OC5F IC1F IC2F

01234567

OC1I OC2I IC3ITMSK1 $1022OC3I OC4I OC5I IC1I IC2I

01234567

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Inputs: Pulse Accumulator

• The pulse accumulator is an 8-bit counter(read and writeable)

• It will count the # of pulses coming intoPA7 when configured to do so

• It can also be used to measure the pulsewidth

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• PACNT $1027 – 8 Bit PA Count

• PACTL $1026 – Data Direction for PA7 Pin

– PA Enable

– PA Mode

– PA Edge

B7 B0

B6 B5

PA ENPA

MOD

PAEDGE

B4

DDR A7

B7

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• TFLG2 $1025 – PA Overflow Flag

– PA Input Edge Flag

• TMSK2 $1024 – PA Overflow Interrupt Enable

– PA Input Edge InterruptEnable

PA

OVF

PA

IF

B4B5

PA

OVI

PA

II

B4B5

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Inputs

• Applications:

– User input (buttons, etc.)

– Counting events (products on an assembly

line with pulse accumulator)

– Length of input (how long a button is held)

• Morse Code

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Outputs: Output Compare

•For Output Compare 2-5, Each Compare Registercontrols a single pin

•TCTL1 register determines how each pin changes

when the comparison matches

Output Compare 2 PA6




OM2 OL2 OM3 OL3 OM4 OL4 OM5 OL5 $1020

OMx OLx Pin Configuration

0 0 Do nothing to pin

0 1 Toggle pin on match

1 0 Clear pin on match

1 1 Set pin on match

TCTL1

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Outputs: Output Compare

•When Output Compare is successful it sets correspondingFlag in TFLG1 Control Register:

OC1F OC2F OC3F OC4F OC5F IC1F IC1F IC1FTFLG1

$1023

OutputCompare

1

OutputCompare

2

OutputCompare

3

OutputCompare

4

OutputCompare

5

OC1I OC2I OC3I OC4I OC5I IC1F IC1F IC1FTMSK1

$1022

Output

Compare

1

Output

Compare

2

Output

Compare

3

Output

Compare

4

Output

Compare

5

•It can also generate an interrupt if the appropriate mask bits are

set

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Outputs: Real-Time Interrupt

• Similar to the prescalar concept

• Generates hardware interrupts at one offour fixed rates

• Sets a flag at each interrupt• Easier to use than generating output

comparisons each time

• Limited to only 4 specific rates

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Outputs: Real-Time Interrupt

• TMSK2 $1024

– Real-Time InterruptEnable

• TFLG2 $1025

– Real-Time InterruptFlag

• PACTL $1026 – Real-Time Interrupt

Rate Selects

RTII

B6

RTIF

B6

B0

RTR0RTR1

B1

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Outputs: Real-Time Interrupts

For 8MHz Crystal Frequency

(2MHz E Clock)

RTR1 RTR0 E/2

13

Divided By RTI Rate RTI Frequency

0 0 1 4.10 ms 244 Hz

0 1 2 8.19 ms 122 Hz

1 0 4 16.38 ms 61.0 Hz

1 1 8 32.77 ms 30.5 Hz

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Outputs

• Applications:

– Pulse Width Modulation with OutputCompares

– Create a delay, but use the wait productively• Read the clock time

• Create an output compare with an offset

– Drive a stepper motor with RTI

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References/ Acknowledgements

• http://www.briticanna.com/clockworks

• http://www.me.gatech.edu/mechatronics_lab/

• http://www.uoguelph.ca/~antoon/gadgets/555/55

5.html• http://www.electronics-

tutorials.com/devices/555.htm

• http://www.williamson-labs.com/480_555.htm• The “Crazy J” Groups Timer Slides

• M68HC11 Reference Manual

Date post:	03-Jun-2018
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