assembally code register addressing

toblerone

dunno if anyone here does embedded programming, if ya do Ive a little knot I need some help with
Im working with a 87C552, an 8051 derivative, and am reading a number from a keypad to use as an Id to select a servo motor to run PWM to.
1) I have the keypad scan function saving the kay value to the accumulator.
2) I have the current PWM value for each of the 5 motors stored in registers 1 to 5

How do I use the number in the accumulator to select the information in the relevant register?
IE
if A = 3
then
move data from R3 to PWM0

Red Alert

think you might have a prob here. you sure you need to use the registers as you could use indexed addressing on the main memory much easier.

toblerone

for anyone interested this is how I did it, the code needed overall restructre and I still didnt get around to working out the exact PWM values, but theese will be XTAL and servo specific (I used a 16MHz XTAL)

Well it was gonna go hear but board post size restrictions stopped me, cos its to long.
If ya wanna know post to that effect and I'll split it up to vbulletin freindly bitesize chunks!

finnpark

Maybe I am missing something but can you not do this:

MOV B,A ; Stores ACC in B reg

ANL A,#03H ; Puts everything else to 0

CJNE A,#03H,NOT_THREE ;Compares acc to 3(hex and dec the same for 3)-;COMPARE JUMP TO LABEL IF NOT EQUAL ELSE GO TO NEXT LINE IF EQUAL

MOV PWM0,R3

MOV A,B ;Puts value back in A

;rest of program
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NOT_THREE: MOV A,B

;rest of program
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toblerone

i actually did something very like that here is one of the subroutines that used a checking matrix:

loadValue:
/********************************************************
*	This function uses the keyID in the ACC, to	*
*select the correct register from which it obtains the 	*
*corresponding current motor's PWM value and loads it to*
*the PWM0. Then returns					*
********************************************************/
	
	CJNE A, #01H, mov1skip	/*IF 1 COPY FROM R1*/
	MOV PWM0, R1		/*MOV CURRENT M1 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov1skip:
	CJNE A, #02H, mov2skip	/*IF 2 COPY FROM R2*/
	MOV PWM0, R2		/*MOV CURRENT M2 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov2skip:
	CJNE A, #03H, mov3skip	/*IF 3 COPY FROM R3*/
	MOV PWM0, R3		/*MOV CURRENT M3 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov3skip:
	CJNE A, #04H, mov4skip	/*IF 4 COPY FROM R4*/
	MOV PWM0, R4		/*MOV CURRENT M4 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov4skip:
	CJNE A, #05H, mov5skip	/*IF 5 COPY FROM R5*/
	MOV PWM0, R5		/*MOV CURRENT M5 VALUE TO PWM0*/
	JMP endSkip
mov5skip:
	CJNE A, #06H, mov6skip	/*IF 6 COPY FROM R1*/
	MOV PWM0, R1		/*MOV CURRENT M1 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov6skip:
	CJNE A, #07H, mov7skip	/*IF 7 COPY FROM R2*/
	MOV PWM0, R2		/*MOV CURRENT 2 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov7skip:
	CJNE A, #08H, mov8skip	/*IF 8 COPY FROM R3*/
	MOV PWM0, R3		/*MOV CURRENT M3 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov8skip:	
	CJNE A, #09H, mov9skip	/*IF 9 COPY FROM R4*/
	MOV PWM0, R4		/*MOV CURRENT M4 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
mov9skip:
	CJNE A, #10H, endSkip	/*IF 10 COPY FROM R5*/
	MOV PWM0, R5		/*MOV CURRENT M5 VALUE TO PWM0*/
	JMP endSkip		/*JUMP TO END OF FUNCTION*/
endSkip:RET			/*RETURN TO MAIN*/