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Timers and ATDFeatures Covered

Timers

Input CaptureATD

Features Not Covered

Pulse AccumulatorOC7 Data Output

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Timer Modes

For TimersFor External Interrupt Generation

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Turning on the timer

Set to 1 to enable

Clock counts in TCNT

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Creating a regular time interrupt 1

Clock prescale @ 8MHzResolution = 125ns X Prescale Factor

Max Duration = 125ns X Prescale Factor X (2^16)

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Interrupt Triggering

Set to one to enable interrupt for that port

Write a One to clear the interrupt flag

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Scheduling an Interrupt

Must be in output compare mode.

Store the time to interrupt in thecorresponding TC register.

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In the interrupt handler Clear the interrupt by writing a

1 to the correct bit in TFLG1.

Schedule the next interrupt

relative to the TC, not theTCNT.

Note, the example code

schedules future interrupts off

of the TCNT, which will cause

the period to drift due tointerrupt handling time.

Movb #$80,TFLG1 ;clear C7F

FLG1

;Schedule Next T7

Interrupt

ldd TC7H ;Load Timer Counter

into D

addd T7RATE ;Add T7RATE to D

std TC7H ;Store D to TC7H

bsr work ;do actual work

rti

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Automatic Actions

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Example 5ms clockT7RATE equ #1250 ;1250 / 250KHz = 5ms

sei ;set interrupt mask - disable interrupts

movw #Timer7IRQ,Timer7vec ;Load Address of Timer7IRQ into vector

movb #$05,TMSK2 ;Prescalar = /32 = 250KHz clock

movb #$80,TIOS ;Set Timer 7 and Timer 6 to output compare

movb #$80,TCTL1 ;Set Timer 7 and Timer 6 output to toggle

movb #$80,TMSK1 ;Enable interrupt for Timer 7

; Schedule first interupt Relative to TCNT

ldd TCNTH ;Load Timer Counter into D

addd T7RATE ;Add T7RATE to D

std TC7H ;Store D to TC7H

;Schedule Timer 6 Interrupts

movb #$80,TSCR ;Enables timers

;do nothing else before enabling interupts

cli ;clear interrupt mask - enable interru

Timer7IRQ

Movb #$80,TFLG1 ;clear C7F FLG1

;Schedule Next T7 Interrupt

ldd TC7H ;Load Timer Counter into D

addd T7RATE ;Add T7RATE to D

std TC7H ;Store D to TC7H

rti

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Input Capture

Bit in TIOS should be clear

Select which edge to trigger on in

When the edge occurs, an input is generated(if enabled) and the current TCNT is copiedinto the TC for that port.

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ATD

Benefits over external ATD

Easier to set up, less wiring.

More accurate ( up to 10 bits ).

You get 8 channels ( 0 7 ).

Still have to level shift to between 0 and 5V

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Proper Configuration

SignalSource

Conditioning

+

-

68HC12

0~5V

R

For Low Frequency Signals

Add a resistor to protect HC12 in case

input goes above 5V or less than ground.

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Powering On the ATD

Write a 1 here

Allow 100us to stabilizeOther Bits ControlATD Interrupts

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Select Time per sample

Sets 10 Bit mode when 1

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Choose What to sample

4 Or 8 Conversions

Run Continuously?

Divide Conversions between registers?

Which Ports to run conversion on

Sample Values

$70 -Continuously do one conversion on each ATD port

$67 -Continuously do 8 conversion sequences on port 7

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Getting the Results

Read ADRnH to get 8 ( or 10 ) bits of ATD

data Most significant 8 bits in ADRnH,

lower two bits in ADRnL.

If the flag in ATDSTAT is 1, the conversion

is complete.