include "1200def.inc"
.device AT90S1200
.equ INPUT =2 PD2
.equ SYS_ADDR =0 The system address
.def S =R0
.def inttemp =R1
.def ref1 =R2
.def ref2 =R3
.def temp =R16
.def timerL =R17
.def timerH =R16
.def system =R19
.def command =R20
.def bitcnt =R21
cseg
.org 0
rjmp reset
;********************************************************************
;* "TIM0_OVF" - Timer/counter overflow interrupt handler
;*
;* The overflow interrupt increments the "timerL" and "timerH"
;* every 64us and 16,384us.
;*
;* Number of words: 7
;* Number of cycles: 6 + reti
;* Low registers used: 1
;* High registers used: 3
;* Pointers used: 0
;********************************************************************
.org OVF0addr
TIM0_OVF: in S,sreg
inc timerL Updated every 64us
inc inttemp
brne TIM0_OVF_exit
inc timerH
TIM0_OVF_exit: out sreg,S
reti
;********************************************************************
;* Example program
;*
;* Initializes timer, ports and interrupts.
;*
;* Calls "detect" in an endless loop and puts the result out on
;* port B.
;*
;* Number of words: 16
;* Low registers used: 0
;* High registers used: 3
;* Pointers used: 0
;********************************************************************
reset: ldi temp,low(RAMEND) Initialize stackpointer
out SPL,temp
ldi temp,high(RAMEND) Commented out since 1200 does not hae SRAM
out SPH,temp
ldi temp,1 Timer/Counter 0 clocked at CK
out TCCR0,temp
ldi temp,1<<TOIE0 Enable Timer0 overflow interrupt
out TIMSK,temp
ser temp PORTB as output
out DDRB,temp
sei Enable gobal iterrupt
main: rcall detect Call RC5 detect routine
cpi system,SYS_ADDR Respponds only at the specified address
brne release
andi command,0x3F Remove control bit
out PORTB,command
rjmp main
release: clr command Clear PORTB
out PORTB,command
rjmp main
;********************************************************************
;* "detect" - RC5 decode routine
;*
;* This subroutine decodes the RC5 bit stream applied on PORTD
;* pin "INPUT".
;*
;* If successe: The command and system address are
;* returned in "command" and "system".
;* Bit 6 of "command" holds the toggle bit.
;*
;* If failed: $FF in both "system" and "command"
;*
;* Crystal frequency is 4MHz
;*
;* Number of words: 72
;* Low registers used: 3
;* High registers used: 6
;* Pointers used: 0
;********************************************************************
detect: clr inttemp
clr timerH
detect1: clr timerL
detect2: cpi timerH,8 If line not idle within 131ms
brlo dl1
rjmp fault then exit
dl1: cpi timerL,55 If line low for 3.5ms
brge start1 then wait for start bit
sbis PIND,INPUT If line is
rjmp detect1 low - jump to detect1
rjmp detect2 high - jump to detect2
start1: cpi timerH,8 If no start bit detected
brge fault within 130ms then exit
sbic PIND,INPUT Wait for start bit
rjmp start1
clr timerL Measure length of start bit
start2: cpi timerL,17 If startbit longer than 1.1ms,
brge fault exit
sbis PIND,INPUT
rjmp start2
Positive edge of 1st start bit
mov temp,timerL timer is 1/2 bit time
clr timerL
mov ref1,temp
lsr ref1
mov ref2,ref1
add ref1,temp ref1 = 3/4 bit time
lsl temp
add ref2,temp ref2 = 5/4 bit time
start3: cp timerL,ref1 If high periode St2 > 3/4 bit time
brge fault exit
sbic PIND,INPUT Wait for falling edge start bit 2
rjmp start3
clr timerL
ldi bitcnt,12 Receive 12 bits
clr command
clr system
sample: cp timerL,ref1 Sample INPUT at 1/4 bit time
brlo sample
sbic PIND,INPUT
rjmp bit_is_a_1 Jump if line high
bit_is_a_0: clc Store a '0'
rol command
rol system
Synchronize timing
bit_is_a_0a: cp timerL,ref2 If no edge within 3/4 bit time
brge fault exit
sbis PIND,INPUT Wait for rising edge
rjmp bit_is_a_0a in the middle of the bit
clr timerL
rjmp nextbit
bit_is_a_1: sec Store a '1'
rol command
rol system
Synchronize timing
bit_is_a_1a: cp timerL,ref2 If no edge within 3/4 bit time
brge fault exit
sbic PIND,INPUT Wait for falling edge
rjmp bit_is_a_1a in the middle of the bit
clr timerL
nextbit: dec bitcnt If bitcnt > 0
brne sample get next bit
;All bits sucessfully received!
mov temp,command Place system bits in "system"
rol temp
rol system
rol temp
rol system
bst system,5 Move toggle bit
bld command,6 to "command"
Clear remaining bits
andi command,0b01111111
andi system,0x1F
ret
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