Advanced Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 195

Example 4.16
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Write a program to generate a two-tone siren that alternates between 250 Hz and 500 Hz
with each siren tone lasting half of a second.
Solution:

#include “c:\miniide\hcs12.inc”

org $1500

start lds #$1500

bset DDRT,BIT5 ; configure PT5 pin for output

forever ldx #250 ; repeat 500 Hz waveform 250 times

tone1 bset PTT,BIT5 ; pull PT5 pin to high

ldy #1

jsr delayby1ms

bclr PTT,BIT5

ldy #1

jsr delayby1ms

dbne x,tone1

ldx #125 ; repeat 250 Hz waveform for 125 times

tone2 bset PTT,BIT5

ldy #2

jsr delayby1ms

bclr PTT,BIT5

ldy #2

jsr delayby1ms

dbne x,tone2

bra forever

#include “c:\miniide\delay.asm”

; org $FFFE ; uncomment this line for CodeWarrior

; dc.w start ; uncomment this line for CodeWarrior

end

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4.11.4 Interfacing with DIP Switches
A switch is probably the simplest input device we can find. To make input more efficient, a
set of eight switches organized as a dual inline package (DIP) is often used. A DIP package can
be connected to any input port with eight pins, such as Port A, Port B, and Port H, as shown in
Figure 4.19. When a switch is closed, the associated Port A pin input is 0. Otherwise, the associ-
ated Port A pin has a value of 1. Each Port A pin is pulled up to high via a 10-k Ω resistor when

the associated switch is open.

Example 4.17
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Write a sequence of instructions to read the value from an eight-switch DIP connected to
Port A of the HCS12 into accumulator A.
Solution:
#include “c:\miniide\hcs12.inc”

movb #$0,DDRA ; configure Port A for input

ldaa PTA

…

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