Basic DC Motor Control

MOV TMOD, #50H ; put timer 1 in event counting mode
SETB TR1 ; start timer 1
MOV DPL, #LOW(LEDcodes) ; | put the low byte of the start address of
	; the
	; | 7-segment code table into DPL

MOV DPH, #HIGH(LEDcodes) ; put the high byte into DPH

CLR P3.4 ; |
CLR P3.3 ; | enable Display 0

again:
	CALL setDirection ; set the motor's direction
	MOV A, TL1 ; move timer 1 low byte to A
	CJNE A, #10, skip ; if the number of revolutions is not 10 skip
		; next instruction
	CALL clearTimer ; if the number of revolutions is 10, reset
		; timer 1

skip:
	MOVC A, @A+DPTR ; | get 7-segment code from code table - the
		; index into the table is
		; | decided by the value in A
		; | (example: the data pointer points to the
		; start of the
		; | table - if there are two revolutions, then
		; A will contain two,
		; | therefore the second code in the table
		; will be copied to A)
	MOV C, F0 ; move motor direction value to the carry
	MOV ACC.7, C ; and from there to ACC.7 (this will ensure
		; Display 0's decimal point
		; will indicate the motor's direction)
	MOV P1, A ; | move (7-seg code for) number of
		; revolutions and motor direction
		; | indicator to Display 0
	JMP again ; do it all again

setDirection:
	PUSH ACC ; save value of A on stack
	PUSH 20H ; save value of location 20H (first bit-
		; addressable
		; location in RAM) on stack
	CLR A ; clear A
	MOV 20H, #0 ; clear location 20H
	MOV C, P2.0 ; put SW0 value in carry
	MOV ACC.0, C ; then move to ACC.0
	MOV C, F0 ; move current motor direction in carry
	MOV 0, C ; and move to LSB of location 20H (which has
		; bit address 0)
	CJNE A, 20H, changeDir ; | compare SW0 (LSB of A) with F0 (LSB of
		; 20H)
		; | - if they are not the same, the motor's
		; direction needs to be reversed
	JMP finish ; if they are the same, motor's direction does
		; not need to be changed

changeDir:
	CLR P3.0 ; |
	CLR P3.1 ; | stop motor
	CALL clearTimer ; reset timer 1 (revolution count restarts
		; when motor direction changes)
	MOV C, P2.0 ; move SW0 value to carry
	MOV F0, C ; and then to F0 - this is the new motor
		; direction
	MOV P3.0, C ; move SW0 value (in carry) to motor control
		; bit 1
	CPL C ; invert the carry
	MOV P3.1, C ; | and move it to motor control bit 0 (it
		; will therefore have the opposite
		; | value to control bit 1 and the motor willfinish:

finish:
	POP 20H ; get original value for location 20H from the
		; stack
	POP ACC ; get original value for A from the stack
	RET ; return from subroutine
clearTimer:
	CLR A ; reset revolution count in A to zero
	CLR TR1 ; stop timer 1
	MOV TL1, #0 ; reset timer 1 low byte to zero
	SETB TR1 ; start timer 1
	RET ; return from subroutine
		; | this label points to the start address of the 7-segment code table which is
		; | stored in program memory using the DB command below

LEDcodes:

DB 11000000B, 11111001B, 10100100B, 10110000B, 10011001B, 10010010B, 10000010B, 11111000B, 10000000B, 10010000B

Laboratory Report: Click here to download the file