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;**** A P P L I C A T I O N N O T E A V R 1 2 8 ************************
;*
;* Title: Setup and Use the Analog Comparator
;* Version: 1.1
;* Last updated: 97.07.04
;* Target: AT90Sxxxx (Devices with Analog Comparator)
;*
;* Support E-mail: avr@atmel.com
;*
;* DESCRIPTION:
;* This Application note shows how to enable and use some features of the
;* AVR's on-board precision Analog Comparator.
;*
;* The Application note is written as a program example performing the
;* following tasks:
;*
;* - Wait for a positive output edge by polling the comparator output
;* - Wait for a positive output edge by polling the interrupt flag
;* - Enable interrupt on comparator output toggle. The interrupt routine
;* increments a 16 bit register counter each time it is executed
;*
;***************************************************************************
.include "1200def.inc"
;***** Global Register Variables
.def temp=r16 ;temporary storage register
.def cntL=r17 ;register counter low byte
.def cntH=r18 ;register counter high byte
;***** Interrupt Vectors
rjmp RESET ;Reset Handle
.org ACIaddr
rjmp ANA_COMP ;Analog Comparator Handle
;***************************************************************************
;*
;* "ANA_COMP"
;*
;* This interrupt routine is served each time ACI in the ACSR register is
;* set, provided that the Analog Comparator interrupt is enabled (ACIE is
;* set). The routine increments a 16-bit counter each time it is run
;*
;* Number of words :5
;* Number of cycles :8
;* Low registers used :1 (ac_tmp)
;* High registers used :2 (cntL,cntH)
;*
;***************************************************************************
;***** Interrupt Routine Register Variables
.def ac_tmp=r0 ;temporary storage register for SREG
;***** Code
ANA_COMP:
in ac_tmp,SREG ;temporarily store the Status register
subi cntL,low(-1)
sbci cntH,high(-1) ;counter = counter + 1
out SREG,ac_tmp ;restore Status register
reti
;***************************************************************************
;*
;* PROGRAM EXECUTION STARTS HERE
;*
;***************************************************************************
RESET:
;***** Include if used on device with RAM
; ldi temp,low(RAMEND)
; out SPL,temp
; ldi temp,high(RAMEND)
; out SPH,temp
;***************************************************************************
;*
;* "wait_edge1"
;*
;* This piece of code waits until the output of the comparator (the ACO-bit
;* in ACSR) goes high. This way of doing it requires no setup, however,
;* extremely short pulses can be missed, since the program runs three clock
;* cycles between each time the comparator is checked. Another disadvantage
;* is that the program has to wait for the output to be come negative first,
;* in case the output is positive when polling starts.
;*
;* Number of words :4
;* Number of cycles :4 per loop. Response time: 3 - 5 clock cycles
;* Low registers used :None
;* High registers used :None
;*
;***************************************************************************
;***** Code
wait_edge1:
sbic ACSR,ACO ;if output is high
rjmp wait_edge1 ;wait
we1_1:
sbis ACSR,ACO ;if output is low
rjmp we1_1 ;wait
;***************************************************************************
;*
;* "wait_edge2"
;*
;* This piece of code waits until the output of the comparator (the ACO-bit
;* in ACSR) goes high. This is a more secure solution, since the interrupt
;* flag is polled. This allows the user to insert code within the wait loop
;* because hardware "remembers" pulses of shorter duration than the polling
;* interval. Another positive feature is that there is no need to wait for
;* a preceeding negative edge.
;*
;* Number of words :5
;* Number of cycles :Inital setup :2
;* Flag clearing:1
;* Loop :4
;* Response time:3 - 5
;* Low registers used :None
;* High registers used :None
;*
;***************************************************************************
;***** Code
wait_edge2:
;***** Initial Hardware setup (assumes ACIE = 0 from reset)
sbi ACSR,ACIS0
sbi ACSR,ACIS1 ;enable interrupt on rising output edge
;***** Wait
sbi ACSR,ACI ;write a "1" to the ACI flag to clear it
we2_1: ;----------------------- user code goes here
sbis ACSR,ACI ;if ACI is low
rjmp we2_1 ;wait more
;***************************************************************************
;*
;* "ana_init"
;*
;* This code segment enables Analog Comparator Interrupt on output toggle.
;* The program then enters an infinite loop.
;* The 16-bit counter is cleared prior to enabling the interrupt.
;*
;* Performance figures apply to interrupt initialization only.
;*
;* Number of words :4
;* Number of cycles :5
;* Low registers used :None
;* High registers used :1 (temp)
;*
;***************************************************************************
;***** Register Variables
.def temp=r16 ;temporary register
;***** Code
ana_init:
;***** Clear 16-bit counter
clr cntL
clr cntH
;***** Enable Interrupt (assumes ACIE = 0 from reset)
ldi temp,(ACI<<1) ;clear interrupt flag and ACIS1/ACIS0...
out ACSR,temp ;...to select interrupt on toggle
sei ;enable global interrupts
sbi ACSR,ACIE ;enable Analog Comparator interrupt
forever:
rjmp forever
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