Timer Functions - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 380

Start

1. Set OC5 pin action to pull
high
2. Clear C5F flag
3. Start OC5 operation with
delay value equal to 10

Pull the PT5 pin to high
quickly

No

C5F = 0?

Yes

No

HiorLo = 0?
Yes

1. Set OC5 pin action to toggle
2. Set HiorLo flag to 0
3. Start a new OC5 operation
with delay equal to HiCnt

1. Start a new OC5 operation
With LoCnt as delay
2. HiorLo = 1

Continue to perform other
operations

1. Start a new OC5 operation
With HiCnt as delay
2. HiorLo = 0

Return from interrupt

Figure 8.20 ■ The program logic flow for digital waveform generation

The following assembly program implements this algorithm using the OC5 function:
#include “c:\miniide\hcs12. inc”

HiCnt equ 1200 ; delay count for high interval of the waveform

LoCnt equ 1800 ; delay count for low interval of the waveform

org $1000

HIorLO ds.b 1 ; flag to select HiCnt (1) or LoCnt (0)

org $1500

lds #$1500 ; establish stack pointer

movw #OC5ISR,UserTimerCh5 ; set up OC0 interrupt vector

movb #$90,TSCR1 ; enable TCNT and fast timer flag clear

movb #$03,TSCR2 ; set TCNT clock prescaler to 8

bset TIOS,BIT5 ; enable OC5

movb #$0C,TCTL1 ; configure the OC5 pin action to pull high

ldd TCNT ; start OC5 with delay count equal to 10 and

addd #10 ; pin action to pull high

std TC5

brclr TFLG1,C5F,* ; wait until C5F is set to 1 and PT5 pin pulled high

ldd TC5 ; start another OC5 operation with

addd #HiCnt ; delay count set to HiCnt

std TC5 ; “