Question

Examine the following code and answer the following: 10. Register contents after execution of each instruction Machine code using hand assembly EDSIM51 Simulation a. b. c. istart (origin) at 0 ;load 25H into R5 iload 34H into R7 ;load 0 into A ;add contents of R5 to A now A-A+R5 ; add contents of R7 to A inow A A+R7 ;add to A value 12H ORG OH MOV R5,#25H MOV R7 , #34H MOV A, #0 ADD A, R5 ADD A, R7 ADD A, # 12H HERE: SJMP HEREistay in this loop END ;end of asm source file

Answer 1

Hi,

Please find the solution below and in case any thing is unclear, let me know. (Please note that opcode to machine code mapping is different for different controllers/processors).

Q.)

ORG 0H
MOV R5,#25H
MOV R7,#34H
MOV A,#0
ADD A,R5
ADD A,R7
ADD A,#12H
HERE: SJMP HERE
END

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a.) Relevant register and accumulator values are as follows :

Executed Instruction	R5	R7	ACC	PSW
ORG 0H	0x00	0x00	0x00	0x00
MOV R5,#25H	0x25	0x00	0x00	0x00
MOV R7,#34H	0x25	0x34	0x00	0x00
MOV A,#0	0x25	0x34	0x00	0x00
ADD A,R5	0x25	0x34	0x25	0x01
ADD A,R7	0x25	0x34	0x59	0x00
ADD A,#12H	0x25	0x34	0x6B	0x01
HERE: SJMP HERE	0x25	0x34	0x6B	0x01
END

b.) Machine code(in hex) for the given assembly code (assuming we are working on 8051 microcontroller) would be as follows:

Executed Instruction	Address	OP -> M.C.(HEX)
ORG 0H
MOV R5,#25H	0000	AD 25
MOV R7,#34H	0002	AF 34
MOV A,#0	0004	E5 0
ADD A,R5	0006	ED
ADD A,R7	0007	EF
ADD A,#12H	0008	E5 12
HERE: SJMP HERE	000A	80 000A
END

c.)

EDSIM51 simulation

EdSim51DI- Version 2.1.20 | simple20190501_1.asnm RST Step Pause New Copy Paste System Clock (MHz)12.0 Time: 130us-Instructions: 68 SBUF THO TLO R7 0x34 Ox.00 0x.00 0x00 0x00 ACC 0x6B øøøø l MOV R5 , #25H øøø2 l MOV R7 , #34H 0004 I MOV A, # 0006| ADD A, R5 0007| ADD A,R7 øøø8I ADD A, #12H 0A HERE: SJMP HERE 2 PSW 0x01 pins bits 0xFF 0xFF P3 0x00 0x00 DPH Ox00 DPL Ox00 8 0xFF 0xFF P1 0xFF 0xFF PO Data Memory 0x00 0x00 value 0000 00 00 00 00 25 00 34 00 00 00 00 00 00 00 00 1000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 2000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 50 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 6000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Note : Examining the code, we can see that at the end of the code there is an "SJMP" (short-jump) from label "HERE" back to the same label "HERE", thus creating an infinite loop.