How to do 16-Bit Math (AVR ASM)
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;**** A P P L I C A T I O N N O T E A V R 2 0 2 ************************ ;* ;* Title: 16-bit Arithmetics ;* Version: 1.1 ;* Last updated: 97.07.04 ;* Target: AT90Sxxxx (All AVR Devices) ;* ;* Support E-mail: avr@atmel.com ;* ;* DESCRIPTION ;* This application note lists applications for the following ;* Add/Subtract/Compare operations: ;* ;* "add16" ADD 16+16 ;* "adddi16" ADD 16+Immediate(16) ;* "sub16" SUB 16-16 ;* "subi16" SUB 16-Immediate(16) ;* "cp16" COMPARE 16/16 ;* "cpi16" COMPARE 16/Immediate ;* "neg16" NEGATION 16 ;* ;*************************************************************************** .cseg ldi r16,0x12;Set up some registers to show usage of ldi r17,0x34;the subroutines below. ldi r18,0x56;All expected results are presented as ldi r19,0x78;comments ;*************************************************************************** ;* ;* "add16" - Adding 16-bit registers ;* ;* This example adds the two pairs of register variables (add1l,add1h) ;* and (add2l,add2h) The result is placed in (add1l, add1h). ;* ;* Number of words :2 ;* Number of cycles :2 ;* Low registers used :None ;* High registers used :4 ;* ;* Note: The sum and the addend share the same register. This causes the ;* addend to be overwritten by the sum. ;* ;*************************************************************************** ;**** Register Variables .def add1l = r16 .def add1h = r17 .def add2l = r18 .def add2h = r19 ;***** Code add16: add add1l, add2l ;Add low bytes adc add1h, add2h ;Add high bytes with carry ;Expected result is 0xAC68 ;*************************************************************************** ;* ;* "addi16" - Adding 16-bit register with immediate ;* ;* This example adds a register variable (addi1l,addi1h) with an ;* immediate 16-bit number defined with .equ-statement. The result is ;* placed in (addi1l, addi1h). ;* ;* Number of words :2 ;* Number of cycles :2 ;* Low registers used :None ;* High registers used :2 ;* ;* Note: The sum and the addend share the same register. This causes the ;* addend to be overwritten by the sum. ;* ;*************************************************************************** ;***** Register Variables .def addi1l = r16 .def addi1h = r17 ;***** Immediate 16-bit number .equ addi2 = 0x1234 ;***** Code addi16: subi add1l, low(-addi2);Add low byte ( x -(-y)) = x + y sbci add1h, high(-addi2);Add high byte with carry ;Expected result is 0xBE9C ;*************************************************************************** ;* ;* "sub16" - Subtracting 16-bit registers ;* ;* This example subtracts two pairs of register variables (sub1l,sub1h) ;* from (sub2l, sub2h) The result is stored in registers sub1l, sub1h. ;* ;* Number of words :2 ;* Number of cycles :2 ;* Low registers used :None ;* High registers used :4 ;* ;* Note: The result and "sub1" share the same register. This causes "sub1" ;* to be overwritten by the result. ;* ;*************************************************************************** ;***** Register Variables .def sub1l = r16 .def sub1h = r17 .def sub2l = r18 .def sub2h = r19 ;***** Code sub16: sub sub1l,sub2l ;Subtract low bytes sbc sub1h,sub2h ;Add high byte with carry ;Expected result is 0x4646 ;*************************************************************************** ;* ;* "subi16" - Subtracting immediate 16-bit number from a 16-bit register ;* ;* This example subtracts the immediate 16-bit number subi2 from the ;* 16-bit register (subi1l,subi1h) The result is placed in registers ;* subi1l, subi1h. ;* ;* Number of words :2 ;* Number of cycles :2 ;* Low registers used :None ;* High registers used :2 ;* ;* Note: The result and "subi1" share the same register. This causes ;* "subi1" to be overwritten by the result. ;* ;*************************************************************************** ;***** Register Variables .def subi1l = r16 .def subi1h = r17 ;***** Immediate 16-bit number .equ subi2 = 0x1234 ;***** Code subi16: subi subi1l,low(subi2);Subtract low bytes sbci subi1h,high(subi2);Subtract high byte with carry ;Expected result is 0x3412 ;*************************************************************************** ;* ;* "cp16" - Comparing two 16-bit numbers ;* ;* This example compares the register pairs (cp1l,cp1h) with the register ;* pairs (cp2l,cp2h) If they are equal the zero flag is set(one) ;* otherwise it is cleared(zero) ;* ;* Number of words :2 ;* Number of cycles :2 ;* Low registers used :None ;* High registers used :4 ;* ;* Note: The contents of "cp1" will be overwritten. ;* ;*************************************************************************** ;***** Register Variables .def cp1l = r16 .def cp1h = r17 .def cp2l = r18 .def cp2h = r19 ;***** Code cp16: cp cp1l,cp2l;Compare low byte cpc cp1h,cp2h;Compare high byte with carry from ;previous operation ncp16: ;Expected result is Z=0 ;*************************************************************************** ;* ;* "cpi16" - Comparing 16-bit register with 16-bit immediate ;* ;* This example compares the register pairs (cpi1l,cpi1h) with the value ;* cpi2. If they are equal the zero flag is set(one), otherwise it is ;* cleared(zero). This is enabled by the AVR's zero propagation. Carry is ;* also set if the result is negative. This means that all conditional ;* branch instructions can be used after the comparison. ;* ;* Number of words :3 ;* Number of cycles :3 ;* Low registers used :None ;* High registers used :3 ;* ;* ;*************************************************************************** ;***** Register Variables .def cp1l =r16 .def cp1h =r17 .def c_tmp=r18 .equ cp2 = 0x3412 ;Immediate to compare with ;***** Code cpi16: cpi cp1l,low(cp2);Compare low byte ldi c_tmp,high(cp2); cpc cp1h,c_tmp;Compare high byte ;Expected result is Z=1, C= ;*************************************************************************** ;* ;* "neg16" - Negating 16-bit register ;* ;* This example negates the register pair (ng1l,ng1h) The result will ;* overwrite the register pair. ;* ;* Number of words :4 ;* Number of cycles :4 ;* Low registers used :None ;* High registers used :2 ;* ;*************************************************************************** ;***** Register Variables .def ng1l = r16 .def ng1h = r17 ;***** Code ng16: com ng1l ;Invert low byte;Calculated by com ng1h ;Invert high byte;incverting all subi ng1l,low(-1);Add 0x0001, low byte;bits then adding sbci ng1h,high(-1);Add high byte ;one (0x0001) ;Expected result is 0xCBEE ;*************************************************************************** ;* ;* End of examples. ;* ;*************************************************************************** forever:rjmp forever |