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8255 -PPI

Programmable Peripheral Interface

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• Functional configuration of each port is

controlled by the command word.• Control Word Register can only be written

into, no read operation is allowed.

• 8255 offers 3 modes – Mode 0 – Basic I/O

– Mode 1 – Strobed I/O

– Mode 2 –

Strobed bidirectional I/O

• 24 I/O lines organized as 3-ports having 8 I/O

lines each

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8255 MODE INSTRUCTION FORMAT

PORT C (UPPER)1- Input

0- Output

PORT A

1- Input

0- Output

Mode select

0 0 - Mode 0

01 – Mode 1

1X – Mode 2

Mode set

1 – Active

PORT B

1- Input

0- Output

PORT C LOWER)1- Input

0- Output

Mode select0 - Mode 01 – Mode 1

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STEPPER MOTOR• Rotor able to assume discrete stationary angular positions.

• Rotor motion in stepwise-manner from one equilibriumposition to the next.

• Two types of Stepper-Motor.

– Reluctance type

– Permanent Magnet type (PM).

• PM type consists of multiphased stator and two part

permanent magnet rotor.

• Two phase stepper-motor consists of two pairs of stator poles

• Each of 4 poles has its own windings.

• Excitation generates N & S poles at diametrically opposite

side.

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NS

N

S

N

S

NN

S

S

Stepper-Motor Cross-sectional view

N

NN S

SS

Front-ViewRear-View

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• Ns is no. of stator poles

• Nr is no. of pairs of rotor poles

•

3-Schemes for “Stepping” a stepper-Motor1. Wave Scheme.

2. 2-Phase Scheme.

3. Half-Stepping or Mixed Scheme.

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Energizing of Coils in 4-Pole Stepper-

Motor

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Wave SchemeN-Pole

S-Pole

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• A single phase is activated at a time.

• The same number of steps as the full step drive, but the

motor will have significantly less than rated torque. It is rarely

used.

• 30o for each step.

Anticlockwise Clockwise

Step A1 A2 B1 B2 Step A1 A2 B1 B2

1 1 0 0 0 1 1 0 0 02 0 0 0 1 2 0 0 1 0

3 0 1 0 0 3 0 1 0 0

4 0 0 1 0 4 0 0 0 1

Wave Scheme

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2-Phase Scheme

• step angle is 30o but is offset by 15o in the two-phase scheme.

• 12 steps required to move rotor 360o.

Anticlockwise Clockwise

Step A1 A2 B1 B2 Step A1 A2 B1 B2

1 1 0 0 1 1 1 0 1 0

2 0 1 0 1 2 0 1 1 0

3 0 1 1 0 3 0 1 0 1

4 1 0 1 0 4 1 0 0 1

N-Pole

S-Pole

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Stepper Motor Wiring

• Most stepper motors have 6 wires,

however there are motors with 4, 5, or 8

wires also.

• Each of the four coils is made up of one

length of wire with two ends.

• One end is called live and the other end

is called common.

• In a five-wire stepper motor all

four commons are joined together, in a

six-wire stepper motor two pairs

of common wires are joined together, and

in an eight-wire stepper motor none of

the four common wires are joined

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Programming a Stepper

Basics• VLIM-013A supports Stepper motor interface.

• Board consists of 3-parts

1. Address decoding.

2. Stepper-Motor driving circuitry.

3. Operating voltage selections.

8255 PPI0C – Port A0D – Port B0E – Port C0F – Control

Register

TIP 122Darlington pair used

According totorque range

from 2Kg -20Kg12V, 24V, & 6V

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1050:

Software ExperimentsTo run a stepper motor at different speeds

MOV AL, 80H

OUT 0026H, AL

L3: MOV SI,1050H

MOV BL, 04HL2: MOV AL,[SI]

OUT 0020H, AL

CALL L1

INC SI

DEC BL

JNZ L2JMP L3

L1: MOV CX, 0A03

L4: DEC CX

JNZ L4

RET

09H

05H

06H

0AH

INPUT

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To run a stepper motor for required angle within 460o which is

equivalent to 256 steps

MOV AL, 80H

OUT 0026H, AL

MOV CL, 064

L1: MOV SI, 1200H

MOV BL, 04L2: MOV AL,[SI]

OUT 20, AL

DEC CL

JZ L4

MOV DX, 0505

L3: DEC DXJNZ L3

INC SI

DEC BL

JNZ L2

JMP L1

L4: HLT

1200: 09H

05H

06H

0AH

INPUT

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To rotate the motor in both forward and reverse direction

MOV AL, 80H

OUT 0026H, AL

L1: MOV CL, 050

FWD: MOV SI, 1200H

CALL ROTATE

DEC CLJNZ FWD

CALL DELAY

MOV CL, 050

REV: MOV SI, 1300H

CALL ROTATE

DEC CLJNZ REV

CALL DELAY

JMP L1

ROTATE: MOV BL,04

L2: MOV AL, [SI]

OUT 0020,AL

MOV DX, 0505L3: DEC DX

JNZ L3

INC SI

DEC BL

JNZ L2

RET

DELAY: MOV DX, 0FFF

L4: DEC DX

JNZ L4

RET

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1200: 09H 05H 06H 0AH

INPUT

1300: 0AH 06H 05H 09H

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419408_634124997373765000 (1)

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