Output Compare Function in ECE 3120: Computer Systems, Study notes of Microcomputers

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ECE 3120: Computer Systems Chapter 8: ECE-3120-A Musical

Manjeera Jeedigunta

http://blogs.cae.tntech.edu/msjeedigun

Email: [email protected]: 931-372-6181, Prescott Hall 120

Output Compare Function †^

The HCS12 has eight output compare functions.

†^

Each output compare channel consists of „^

A 16-bit comparator „^

A 16-bit compare register TCx (also used as inout captureregister) „^

An output action pin (PTx, can be pulled high, pulled low,or toggled) „^

An interrupt request circuit „^

A forced-compare function (CFOCx) „^

Control logic

7

6

5

4

3

2

1

0

OM^

OL^

OM^

OL^

OM^

OL^

OM^

OL

valueafter reset

0

0

0

0

0

0

0

0

(^7) read: anytimewrite: anytime Figure 8.18 Timer control register 1 and 2 (TCTL1 & TCTL2)

6

5

4

3

2

1

0

OM^

OL^

OM^

OL^

OM^

OL^

OM^

OL

0

0

0

0

0

0

0

0

(a) TCTL1 register(b) TCTL2 register valueafter reset

OMn OLn : output level^0011

0 1 0 1

no action (timer disconnected from output pin)toggle OCn pinclear OCn pin to 0set OCn pin to high

†^

The action is determined by the Timer Control Register 1 & 2 (TCTL1& TCTL2):

†^

A successful compare will set the corresponding flag bit in the TFLG1register.

†^

An interrupt may be optionally requested if the associated interruptenable bit in the TIE register is set.

Operation of the Output-Compare Function

HCS12DP

PT

3.3^ μF

Buzzer

Figure 8.21 Circuit connection for a buzzer

Making Sound Using the Output-Compare Function^ †^

A sound can be generated by creating a digital waveform withappropriate frequency and using it to drive a speaker or abuzzer. †^

The circuit connection for a buzzer is shown in Figure 8.21. †^

The simplest song is a two-tone siren.

#include

"c:\miniide\hcs12.inc"

hi_freq

equ

; delay count for 1200 Hz (with 1:8 prescaler)

lo_freq

equ

; delay count for 300 Hz (with 1:8 prescaler)

toggle

equ

$^

; value to toggle the TC5 pin

org^

delay

ds.w

; store the delay for output-compare operation

org^

lds^

movw

#oc5_isr,UserTimerCh5 ; initialize the interrupt vector entry movb

#$90,TSCR

; enable TCNT, fast timer flag clear

movb

#$03,TSCR

; set main timer prescaler to 8

†^

Example 8.7 Write a program to generate a two-tone sirenthat oscillates between 300 Hz and 1200 Hz. †^

Solution: „^

Set the prescaler to TCNT to 1:8.

„^

The delay count for the low frequency tone is (

÷^ 8)

÷^300

÷

„^

The delay count for the high frequency tone is (

÷^ 8)

÷^1200

÷^ 2 = 1250.

bset

TIOS,OC

; enable OC

movb

#toggle,TCTL

; select toggle for OC5 pin action

movw

#hi_freq,delay

; use high frequency delay count first

ldd^

TCNT

; start the low frequency sound

addd

delay

;^

std^

TC

;^

bset

TIE,OC

; enable OC5 interrupt

cli^

;^

forever

ldy

#^

; wait for half a second

jsr^

delayby100ms

;^

movw

#lo_freq,delay ; switch to low frequency delay count ldy^

jsr^

delayby100ms movw

#hi_freq,delay ; switch to high frequency delay count bra^

forever

oc5_isr

ldd

TC

addd

delay std^

TC

rti #include c:\miniide\delay.asm”

end

#include

"c:\miniide\hcs12.inc"

G^

equ^

; delay count to generate G3 note (with 1:8 prescaler)

B^

equ^

; delay count to generate B3 note (with 1:8 prescaler)

C^

equ^

; delay count to generate C4 note (with 1:8 prescaler)

C4S

equ^

; delay count to generate C4S (sharp) note

D^

equ^

; delay count to generate D4 note (with 1:8 prescaler)

E^

equ^

; delay count to generate E4 note (with 1:8 prescaler)

F^

equ^

; delay count to generate F4 note (with 1:8 prescaler)

F4S

equ^

; delay count to generate F4S note (with 1:8 prescaler)

G^

equ^

; delay count to generate G4 note (with 1:8 prescaler)

A^

equ^

; delay count to generate A4 note (with 1:8 prescaler)

B4F

equ^

; delay count to generate B4F note (with 1:8 prescaler)

B^

equ^

; delay count to generate B4 note (with 1:8 prescaler)

C^

equ^

; delay count to generate C5 note (with 1:8 prescaler)

D^

equ^

; delay count to generate D5 note (with 1:8 prescaler)

E^

equ^

; delay count to generate E5 note (with 1:8 prescaler)

F^

equ^

; delay count to generate F5 note (with 1:8 prescaler)

notes

equ

toggle

equ

$^

; value to toggle the TC5 pin

The Star-Spangled Banner

org^

delay

ds.w

; store the delay for output-compare operation

rep_cnt

ds.b

; repeat the song this many times

ip^

ds.b

; remaining notes to be played

org^

lds^

; establish the SRAM vector address for OC

movw

#oc5_isr,UserTimerCh movb

#$90,TSCR

; enable TCNT, fast timer flag clear

movb

#$03,TSCR

; set main timer prescaler to 8

bset

TIOS,OC

; enable OC

movb

#toggle,tctl

; select toggle for OC5 pin action

ldx^

#score

; use as a pointer to score table

ldy^

#duration

; points to duration table

movb

#1,rep_cnt

; play the song once

movb

#notes,ip movw

2,x+,delay

; start with zeroth note

ldd^

TCNT

; play the first note

addd

delay

std^

TC

bset

TIE,C5I

; enable OC5 interrupt

cli^

;^

oc5_isr

ldd

TC

addd

delay std^

TC

rti ; ************************************************************************************ ; The following subroutine creates a time delay which is equal to [Y] times ; 10 ms. The timer prescaler is 1:8. ; ************************************************************************************ delayby10ms

bset

TIOS,OC

; enable OC

ldd^

TCNT

again

addd

; start an output-compare operation

std^

TC

; with 10 ms time delay

wait_lp1 brclr

TFLG1,C0F,wait_lp ldd^

TC

dbne

y,again bclr^

TIOS,OC

; disable OC

rts^

score

dw

D4,B3,G3,B3,D4,G4,B4,A4,G4,B3,C4S

dw^

D4,D4,D4,B4,A4,G4,F4S,E4,F4S,G4,G4,D4,B3,G

dw^

D4,B3,G3,B3,D4,G4,B4,A4,G4,B3,C4S,D4,D4,D

dw^

B4,A4,G4,F4S,E4,F4S,G4,G4,D4,B3,G3,B4,B

dw^

B4,C5,D5,D5,C5,B4,A4,B4,C5,C5,C5,B4,A4,G

dw^

F4S,E4,F4S,G4,B3,C4S,D4,D4,G4,G4,G4,F4S

dw^

E4,E4,E4,A4,C5,B4,A4,G4,G4,F4S,D4,D

dw^

G4,A4,B4,C5,D5,G4,A4,B4,C5,A4,G

; ************************************************************************************** ; Each of the following entries multiplied by 10 ms gives the duration of a note. ; ************************************************************************************** duration dw

dw^

dw^

dw^

dw^

dw^

dw^

dw^

end^