INDUSTRIAL PROCESS CONTROL SYSTEMS
One area where in which microprocessor and microcomputers have a major impact is industrial processor control systems. Process control involves first measuring system variables such as motor speed, temperature, the flow of reactants, the levels of liquids in a tank, thickness of material etc.
The output of controller then adjust the value of each variable until it becomes equal to a predetermined value called set point.
TEMPERATURE CONTROL SYSTEM
The temperature controller can be used to control the temperature of any plant. Typically it contains a Processor unit, Temperature input unit and Control output unit. The 8085 based motherboard forms the processing unit. The Analog-to-Digital unit together with temperature sensor forms the temperature input unit. The relay driver forms the control output unit. Electric power to the heating element (coil) is supplied through relay contacts. The switching ON/OFF of the relay controls the heat supplied to the plant. Operationally, the system requires two set points-upper and lower, to be entered by the user. Whenever the temperature of the plant exceeds the upper limit or recede the lower limit relay is turned-off, so that a temperature is maintained within limits. The software for the temperature controller is developed in 8085 assembly language programs.
HARDWARE DESCRIPTION:
The hardware consists of 8085 microprocessor motherboard, ADC interface board, and relay and driver unit.
The motherboard consists of 8085 MPU, 8KB EPROM, 8KB RAM keyboard and display controller 8279, programmable peripheral interface 8255, 21 key hex-keypad and six numbers of seven segment LED’s. Ports Expansion connector parallel port connectors are provided for external interfacing. The temperature input board or ADC interface board consists of ADC 0809, which is an 8-bit converter with eight channels of input. It is interfaced with the motherboard through 50-pin bus expansion connector. The temperature sensor ADC590 is used to sense the temperature of the plant and its analog output is applied to the channel-0 of ADC.
Relay is switched ON/OFF by driving the transistor to saturation/cut-off which is connected to port A of 8255.

Stepper motor control
Interface a Stepper Motor to the 8085 microprocessor system and write an 8085 assembly language program to control the Stepper Motor.
Basic terminology for stepper motor
STEP ANGLE :- Step is the minimum degree of rotation associated with a single step.
STEPS PER REVOLUTION:- Steps per revolution may be defined as the total number of steps needed to complete 360̊ (e.g. 180 steps × 2 degrees = 360)

steps per second and rpm relation
steps per seconds = rpm ×steps per revolution/ 60
Program
MVI A, 80H ;Initialize 8255 for port A as output.
OUT CR
MVI C, 32H : ;Set repetition count to 50.
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