Example ASM code of how to use SRAM
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;*************************************************************************** ;* PROGRAM ;* Sram ;* DESCRIPTION ;* to show use of SRAM ;* uses the information stored in Sram ;* and outputs the values to portB ;************************************************************************* .include "c:\avrtools\appnotes\8515def.inc" rjmp Init ;************************************************************************** ;* FUNCTION ;* Init ;* DESCRIPTION ;* Intialise the Stackpointer ;* Intialise SRAM ;* Disable the Comparator to save power ;* Intialise Port B for Output ;************************************************************************* Init: ; **** Stack Pointer Setup Code **** ldi r16,$02 ; Stack Pointer Setup out SPH,r16 ; Stack Pointer High Byte ldi r16,$5F ; Stack Pointer Setup out SPL,r16 ; Stack Pointer Low Byte ; **** SRAM Setup Code **** ldi r16,$C0 ; SRAM Access out MCUCR,r16 ; SRAM:SRE bit set, SRW bit set, ; **** Comparator Setup Code **** ldi r16,$80 ; out ACSR,r16 ; Comparator Disabled to save power ; **** Port B Setup Code **** ldi r16,$FF ; I/O Direction Values out DDRB,r16 ; Port B Direction Register ldi r16,$FF ; Init value out PORTB,r16 ; Port B value ;************************************************************************** ;* FUNCTION ;* Main ;* DESCRIPTION ;* Sets up the Y and Z pointer ;* Disable the Comparator to save power ;* sets up R20 with number of elements in the table ;************************************************************************* Main: ldi ZL,$F0 ;init z-pointer low byte clr ZH ;clear z reg high byte ldi ZL,low(TABLE*2);init Z-pointer low byte with TABLE ldi ZH,high(table*2);init Z-pointer High byte with TABLE ldi YL,$60 ;init Y-pointer low byte clr YH ;Clear Y-pointer High byte ldi r20,$08 ;load r20 with 8 decimal ;************************************************************************* ;* FUNCTION ;* Mem ;* DESCRIPTION ;* Stores the information contained in TABLE into SRAM area ;************************************************************************* Mem: lpm ;load constant from program ;memory pointed to by r30:r31 st y+,r0 ;store in SRAM and increment Y-pointer adiw ZL,1 ;increment Z-pointer dec r20 ; subtract 1 from r16 cpi r20,$00 ;compare r20 with 00 brne mem ;if not 00 then loop for more ;************************************************************************* ;* FUNCTION ;* Output ;* DESCRIPTION ;* Re intialises YL ;* Loads r20 with number of elements contained in SRAM ;* Outputs the value from Sram to PortB ;************************************************************************* Output: ldi YL,$60 ;re-init Y-pointer low byte ldi r20,$08 ;load r20 with 8 decimal out_loop: ld r18,y ;load R18 with SRAM loc 60 adiw YL,1 ;increment Y-pointer dec r20 ;decrement r20 out portb,r18 ;output the value to portb rcall delay cpi r20,$00 ;compare R20 with 00 brne out_loop ;if not equal jump to out_loop rjmp output ;if equal jump to output ;to re-init Y-pointer low byte ;************************************************************************** ;* FUNCTION ;* Delay ;* DESCRIPTION ;* delay time for LED's ;************************************************************************* delay: ldi r19,$0a delay1: ldi r16,$80 delay2: ldi r17,$ff delay3: dec r17 brne delay3 dec r16 brne delay2 dec r19 brne delay1 ret ;************************************************************************** ;* FUNCTION ;* Table ;* DESCRIPTION ;* Table holds the values to be stored in SRAM ;************************************************************************* Table: .db $01,$02,$04,$08,$10,$20,$40,$80 |