1. ES C263 Microprocessor Programming and Interfacing
Pawan Sharma Lecture

2. Last Lecture
Instruction Set Architecture

3. Today’s Lecture
Design Example
PC Boot Process

4. Design Example

5. Design a microprocessor based system to control
pH of a solution in a reactor tank.
User enters desired pH (0-14) and controller gain
Reactor tank is provided with three pH sensors, to compute the average pH.
Reactor tank has three inputs.
(acid flow, base flow effluent discharged from factory controlled by valves)
Motorised valve

6. Valve Control
Controlled by stepper motors
1 step is by 1.8 degrees rotation
Valve opening = kP * error
Where error = desired pH – measured pH.
Error positive- close fully acid valve and open base valve accordingly
Error negative- close fully base valve and open acid valve accordingly.
0 – 360 degrees correspond to 0 to 200 steps.

7. Stepper Motor sequence: A B C D 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1
ACW CW
Use a 4- bit port driver (nearly 1 A current)

8. pH sensor
Vout pH 7 14
Voltage output 60mV/pH
-420mV mV

9. Interfacing Analog to Digital Converter
8-bit ADC I0 I7 D0 D7
Start A B C
EOC OE
ALE
ADC 0809

10. Input Keys
Numeric keys 0 – 9
Function keys
pH, kP, enter
Matrix Keypad interfacing!!
- 2 four bit ports.

11. Display Device and storage
Two digit Display
Two seven segment display devices to display pH
Memory Interfacing
ROM (4KB) - FF000H – FFFFFH
SRAM (4K) H – 00FFFH

12. System Block Diagram CPU Memory I/O Interface Parallel I/O Serial I/O
Data
Address
Control

13. Method of Approach
Identify input and output devices
Memory requirements
Suitable memory and I/O interfacing
Assembly Language Programming
Assumptions made

14. PC Boot Process

15. The code performs POST (Power On Self test)
Powered on CPU starts executing code located from FFFF0H – called BIOS and operates in the real mode of operation.
The code performs POST (Power On Self test)
After POST, CPU reads the boot sector
(floppy, hard disk – sequence set in BIOS features)‏
Checks for AA55H at 07DFEH ( Boot signature)‏
The first sector of the bootable disk, contains the boot loader program or the MBR or grub/LILO. The BIOS loads the MBR in RAM starting at address 07C00H and executed.
Loads DL (one of the CPU registers) with
00h if the boot sector was loaded from drive A
80h if the boot sector was loaded from drive C
This way, the bootsector can determine which drive it was booted from.
After the completion of the boot loader program, the control is transferred to the OS.