Problem 1, Digital Camera Design (20pts)

Complete the schematic for this digital camera (this is a purely qualitative exercise). The black circles indicate missing connections. Your job is to choose the most appropriate way to interface the device to microprocessor and to fill any other necessary devices that are missing including those needed for protection. Missing components might include analog amplifiers (single-ended or differential), plain wires, resistors, capacitors, inductors, diodes, and transistors. The shutter is open when the coil is energized and closed otherwise. Give a sentence or two to explain each choice. You don’t need to give sizes or values for the components. Assume that the microprocessor is a variant of the 8051 that has two analog inputs with internal analog to digital converters. You cannot assume that the analog inputs are high impedance.

Common mistakes:

Use of OP-AMP as a power device for driving the coil or for controlling the transistors.
No amplifier, or under-specified amplifier on analog inputs
Lack of protection for coil, 8051 pins.
Attempting to power the coil or flash from 8051 pins or from op-amp.
Direct connection of the shutter button to the shutter drive (no points taken for this)
Use of FET instead of BJT in discharge circuit. This would technically be correct if the flash is above rather than below the device. It might even be a better circuit. (No points taken for this).
Thinking that the motor drive and the coil are somehow separate. The coil is the drive.

Acceptable alternatives:
Use of FET instead of BJT to drive coil and flash
Use of button as pull-up w/ a pull down resistor instead. This is not as good because chip can be damaged if programmer writes a zero to the pin!
Direct control of shutter drive from shutter button. This does not make much sense, but hardware interlocks can be included to prevent picture under low light conditions.

Problem 2: Microcontroller Memory Architecture

A. Explain what the C compiler would have to do to convert this code into 8051 assembly by showing all the necessary segment declarations and explain what goes into each segment. Yes…it is possible. Don’t worry too much about using proper 8051 assembly instructions and directives; just provide pseudo-assembly code for the contents of any code segments, but make sure you are clear about addressing modes and intent (use comments if necessary). (20 pts)

unsigned byte table[8] = {1,2,3,4,5,6,7,8};
int i;

void main() using 0 { // tells compiler to use register bank 0

while (1)

for (i = 0; i<8; i++) {
table[i] = table[i]+1;

P1_0 = ~P1_0;
}

}
// defines interrupt function for external interrupt INT1

void external_handler(void) interrupt 2 using 1 { // register bank 1
P1_0 = ~P1_0;
}

B. Draw the expected waveform on P1.0 if external interrupt int1 were enabled. Assume that the time between dotted lines is equal to one iteration of the inner loop, which is equal to the execution time of the external interrupt handler. (10 pts)

Commong mistakes: not accounting for the delay imposed on the main loop by interrupt processing.

Part A Solution

Common mistakes:

Attempting to initialize the table in the DATA segement instead of in software in the CODE segment
misuse of addressing modes and memory spaces in expressing Tabel[i]= Table[i]+1
Attempting to write to table[] after declaring it to be CONST or CODE

Failure to initialize the stack

Enabling interrupts….this is not implied by the C-code (no points taken for this)
use of MOVC instruction for accessing DATA (no points taken for this)

Alternative: this could have been done using only registers and no data segment for the table. You still would

Have to initialize the table in code.

Segments needed
IDATA for STACK

DS 2 Bytes (I think that is more than enough

IDATA for TABLE

DS 8 Bytes

// reset vector

CSEG AT 0

JMP INIT

// external interrupt 1 vector

CSEG AT 000BH

JMP ISR

CODE RSEG for MAIN

Main: MOV R1,#table; // start at table[0]

Loop: INC @R1;

INC R1;

CJNE R1,#table+8, Loop

ORL P1,1;

JMP Main;

CODE RSET for INIT // could be combined with MAIN segment.

INIT CLR PSW; // set register bank to 0

MOV SP, #STACK-1; // initialize stack

MOV R1, #table // initialize the data table
MOV @R1,#1;

INC R1;

MOV @R1,#2;
…

MOV @R1,#8;
JMP Main;

CODE for interrupt handler

ISR: ORL P1, 1; // no need to protect or modify PSW. Using compiler directive ignored.

RETI