using 8051 microcontroller

;Keyboard subroutine. This program sends the number of key pressed to R7 ;P0.0-P0.3 connected to rows, P0.4-P0.6 connected to columns ; organization as follows: ; ------------- ; row 0 | * | 0 | # | D0 ; ------------- ; row 1 | 7 | 8 | 9 | D1 ; ------------- ; row 2 | 4 | 5 | 6 | D2 ; ------------- ; row 3 | 1 | 2 | 3 | D3 ; ------------- ; c0 c1 c2 ; D6 D5 D4

K1: MOV P0,#01110000B MOV A,P0 ;read all col. (ensure all keys open) ANL A,#01110000B ;masked unused bits CJNE A,#01110000B,K1 ;check til all keys released K2: MOV A,P0 ;see if any key is pressed ANL A,#01110000B ;mask unused bits CJNE A,#01110000B,OVER1 ;key pressed, await closure SJMP K2 ;check if key pressed

MOV P0,011111111B OVER1: CLR P0.0 MOV A,P0 ;read all columns ANL A,#01110000B ;mask unused bits CJNE A,#01110000B,ROW_0 ;key row 0, find the col. SETB P0.0 CLR P0.1 MOV P0,#01111101B ;ground row 1 MOV A,P0 ;read all columns ANL A,#01110000B ;mask unused bits CJNE A,#01110000B,ROW_1 ;keyrow 1, find the col. SETB P0.1 CLR P0.2 MOV P0,#01111011B ;ground row 2 MOV A,P0 ;read all columns ANL A,#01110000B ;mask unused bits CJNE A,#01110000B,ROW_2 ;key row 2, find the col. MOV P0,#01110111B ;ground row 3 MOV A,P0 ;read all columns ANL A,#01110000B ;mask unused bits CJNE A,#01110000B,ROW_3 ;keyrow 3, find the col. LJMP K2 ;if none, false input, repeat ROW_0: MOV DPTR,#KCODE0 ;set DPTR=start of row 0 SJMP FIND ;find col. key belongs to ROW_1: MOV DPTR,#KCODE1 ;set DPTR=start of row 1 SJMP FIND ;find col. key belongs to ROW_2: MOV DPTR,#KCODE2 ;set DPTR=start of row 2 SJMP FIND ;find col. key belongs to ROW_3: MOV DPTR,#KCODE3 ;set DPTR=start of row 3

FIND: RLC A ;skip D7 data (unused) FIND1: RLC A ;see if any CY bit low JNC MATCH ;if zero, get the key number INC DPTR ;point to next col. address SJMP FIND1 ;keep searching MATCH: CLR A ;set A=0 (match is found) MOVC A,@A+DPTR ;get key number from table MOV R7,A ;store pressed key in R7 LJMP K1 ;ASCII LOOK-UP TABLE FOR EACH ROW ORG 300H KCODE3: DB '1','2','3' ;ROW 3 KCODE2: DB '4','5','6' ;ROW 2 KCODE1: DB '7','8','9' ;ROW 1 KCODE0: DB '*','0','#' ;ROW 0 END

8. 10 points) Consider the keypad program attached to this assignment called hw5_keypad.asm" (using the connection as given in the code), what will be the value returned in register R7 for each of the following cases: (a) keys 2 and 5 are pressed simultaneously. (b) keys "4" and "5" are pressed simultaneously. Your answer should be based on analyzing the code and not by using the simulator. Explain your answer for each of the cases given