The FUNCTION subroutine featured in the sample code accepts two 16-bit values as parameters, and also returns a 16-bit value as its result. To complete the challenge for this lab, provide detailed answers to the following questions: 1. What type of operation does the FUNCTION subroutine perform on its two 16-bit inputs? How can you tell? Give a detailed description of the operation being performed by the FUNCTION subroutine. 2. Currently, the two 16-bit inputs used in the sample code cause the brcc EXIT branch to be taken. Come up with two 16-bit values that would cause the branch NOT to be taken, therefore causing the st Z, XH instruction to be executed before the subroutine returns. 3. What is the purpose of the conditionally-executed instruction st Z, XH? ;*********************************************************** .include "m128def.inc" ; Include definition file ;*********************************************************** ;* Internal Register Definitions and Constants ;*********************************************************** .def mpr = r16 .def i = r17 .def A = r18 .def B = r19 ;*********************************************************** ;* Start of Code Segment ;*********************************************************** .cseg ; Beginning of code segment ;*********************************************************** ;* Interrupt Vectors ;*********************************************************** .org $0000 ; Beginning of IVs rjmp INIT ; Reset interrupt .org $0046 ; End of Interrupt Vectors ;*********************************************************** ;* Program Initialization ;*********************************************************** INIT: ; The initialization routine ldi mpr, low(RAMEND) ; initialize Stack Pointer out SPL, mpr ldi mpr, high(RAMEND) out SPH, mpr ;*********************************************************** ;* Main Program ;*********************************************************** MAIN: clr r0 ; *** SET BREAKPOINT HERE *** (#1) dec r0 ; initialize r0 value clr r1 ; *** SET BREAKPOINT HERE *** (#2) ldi i, $04 LOOP: lsl r1 ; initialize r1 value inc r1 lsl r1 dec i brne LOOP ; *** SET BREAKPOINT HERE *** (#3) clr r2 ; *** SET BREAKPOINT HERE *** (#4) ldi i, $0F LOOP2: inc r2 ; initialize r2 value cp r2, i brne LOOP2 ; *** SET BREAKPOINT HERE *** (#5) ; initialize r3 value mov r3, r2 ; *** SET BREAKPOINT HERE *** (#6) ; Note: At this point, you need to enter several values ; directly into the Data Memory. FUNCTION is written to ; expect memory locations $0101:$0100 and $0103:$0102 ; to represent two 16-bit operands. ; ; So at this point, the contents of r0, r1, r2, and r3 ; MUST be manually typed into Data Memory locations ; $0100, $0101, $0102, and $0103 respectively. ; call FUNCTION rcall FUNCTION ; *** SET BREAKPOINT HERE *** (#7) ; infinite loop at end of MAIN DONE: rjmp DONE ;*********************************************************** ;* Functions and Subroutines ;*********************************************************** ;----------------------------------------------------------- ; Func: FUNCTION ; Desc: ??? ;----------------------------------------------------------- FUNCTION: ldi XL, $00 ldi XH, $01 ldi YL, $02 ldi YH, $01 ldi ZL, $04 ldi ZH, $01 ld A, X+ ld B, Y+ add B, A st Z+, B ld A, X ld B, Y adc B, A st Z+, B brcc EXIT st Z, XH EXIT: ret ; return from rcall