Fundamentals of Microcontrollers: Input Capture Timer Function Example - Prof. V. Giurgiut | Study notes Mechanical Engineering

EMCH 367 Fundamentals of Microcontrollers Example INPUT CAPTURE TIMER FUNCTION

EXAMPLE INPUT CAPTURE TIMER FUNCTION

OBJECTIVE

This example has the following objectives:

Review the use of MCU Timer function as an Input Capture (IC) device

Review the use of the free running clock, TCNT, and it overflow flag, TOF

Review the use of a input capture clock, TIC1, and its event flag, IC1F

Demonstrated how the selection of signal transition to be captured is made (here rising edge,

EDG1A) and that the MCU is only sensitive to that particular transition.

Show the calculation of actual time in s from the timer readings, T1, T0, and overflow count,

NOF.

PROGRAM EX_IC

This program is an example of timer input capture. The process is started when a keystroke is received.

Then, the time is measured until a low-high transition is captured on line IC1. In this process, the initial

time, T0, and the capture time, T1, as well as the number of overflows are recorded. After the input

capture, the IC1F flag is reset, the overflow counter is zeroed, and the process is repeated.

FLOWCHART AND CODE

The program flowchart is show to the right of the program instructions. Note the variable definition block

in which T0, T1, and NOF are defined. Next, the initialization block contains reg. X initialization, timer IC

initialization, and SCI initialization. The program loop starts at label BEGIN with the overflow counter,

NOF, being zeroed. First, the RDRF (reception data register full) flag is checked in a loop to verify if a

keystroke has been received. When keystroke was received, the time counter is read and stored in T0.

Then, the programs loops on LABEL1 until and input capture IC1 is recorded. In this loop, TOF is first

check to verify if timer overflow takes place. When timer overflow is detected, the overflow counter,

NOF, is incremented and TOF is reset. Next, IC1F is check to verify if input capture on IC1 took place. If

input capture is not detected, the program returns to LABEL1. When input capture is detected, the

program exits the loop, loads the IC1 timer from TIC1 and stores it in the capture time variable, T1. The

program loops back to the beginning and wait for a new keystroke to restart the process.

The essential code for the program is shown to the right of the program flowchart. This essential code

was incorporated into the standard asm template to generate the file Ex_IC.asm.

Dr. Victor Giurgiutiu Page 111/30/2020

Fundamentals of Microcontrollers: Input Capture Timer Function Example - Prof. V. Giurgiut, Study notes of Mechanical Engineering

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EXAMPLE INPUT CAPTURE TIMER FUNCTION

OBJECTIVE

This example has the following objectives:

 Review the use of MCU Timer function as an Input Capture (IC) device

 Review the use of the free running clock, TCNT, and it overflow flag, TOF

 Review the use of a input capture clock, TIC1, and its event flag, IC1F

 Demonstrated how the selection of signal transition to be captured is made (here rising edge,

EDG1A) and that the MCU is only sensitive to that particular transition.

 Show the calculation of actual time in s from the timer readings, T1, T0, and overflow count,

NOF.

PROGRAM EX_IC

This program is an example of timer input capture. The process is started when a keystroke is received.

Then, the time is measured until a low-high transition is captured on line IC1. In this process, the initial

time, T0, and the capture time, T1, as well as the number of overflows are recorded. After the input

capture, the IC1F flag is reset, the overflow counter is zeroed, and the process is repeated.

FLOWCHART AND CODE

The program flowchart is show to the right of the program instructions. Note the variable definition block

in which T0, T1, and NOF are defined. Next, the initialization block contains reg. X initialization, timer IC

initialization, and SCI initialization. The program loop starts at label BEGIN with the overflow counter,

NOF, being zeroed. First, the RDRF (reception data register full) flag is checked in a loop to verify if a

keystroke has been received. When keystroke was received, the time counter is read and stored in T0.

Then, the programs loops on LABEL1 until and input capture IC1 is recorded. In this loop, TOF is first

check to verify if timer overflow takes place. When timer overflow is detected, the overflow counter,

NOF, is incremented and TOF is reset. Next, IC1F is check to verify if input capture on IC1 took place. If

input capture is not detected, the program returns to LABEL1. When input capture is detected, the

program exits the loop, loads the IC1 timer from TIC1 and stores it in the capture time variable, T1. The

program loops back to the beginning and wait for a new keystroke to restart the process.

The essential code for the program is shown to the right of the program flowchart. This essential code

was incorporated into the standard asm template to generate the file Ex_IC.asm.

Instructions

i) Define variables:

a. Origin of time, T0 = 2 bytes

b. Capture time, T1 = 2 bytes

c. Overflow counter, NOF1 = 1

byte

ii) Initialize

iii) Initialize index X to REGBAS

iv) Initialize timer IC1 function: set

EDG1A in TCTL

v) Initialize SCI

vi) Wait for a keystroke reception

vii) Store initial time

viii) Zero overflow counter NOF

ix) Reset TOF

x) Wait for the input capture

xi) Check TOF

xii) Jump if no TOF; else

a. Increment overflow counter

b. Reset TOF

xiii) Check IC1F

xiv) Loop back

xv) After input capture

xvi) Load and store t

xvii) Reset IC1F by writing 1 to it

xviii) Loop back to iii) and do it again

Flowchart

SWI

LABEL

START

NOP

BEGIN

LABEL

LABEL

N

Y

N

Y

Code

ORG DATA

T0 RMB 2

T1 RMB 2

NOF1 RMB 1

ORG PROGRAM

START LDX #REGBAS

LDAA #%

STAA TCTL2,X