Stepper Motor Control - Free 8085 Microprocessor projects

As port A is used as an output port, control word for 8255 is 80H.

Stepper Motor Control Program:

6000H Excite code DB 03H, 06H,

09H, OCH : This is the code sequence for clockwise rotation

Subroutine to rotate a stepper motor clockwise by 360° - Set the counts:

MVI C, 32H : Set repetition count to 50ıο

START: MVI B, 04H : Counts excitation sequence

LXI H, 6000H : Initialize pointer

BACK1: MOV A, M : Get the Excite code

OUT PORTA : Send Excite code

CALL DELAY : Wait

INX H : Increment pointer

DCR B : Repeat 4 times

JNZ BACK l

DCR C

JNZ START : Repeat 50 times

RET

A stepper motor is a digital motor. It can be driven by digital signal. Fig. shows the typical 2 phase motor rated 12V /0.67 A/ph interfaced with the 8085 microprocessor system using 8255. Motor shown in the circuit has two phases, with center-tap winding. The center taps of these windings are connected to the 12V supply. Due to this, motor can be excited by grounding four terminals of the two windings. Motor can be rotated in steps by giving proper excitation sequence to these windings. The lower nibble of port A of the 8255 is used to generate excitation signals in the proper sequence. These excitation signals are buffered using driver transistors. The transistors are selected such that they can source rated current for the windings. Motor is rotated by 1.80 per excitation.