MIT-Curricular/ES/Project/report.md

LPC1768 Multi-Base Calculator - Code Explainer & Hardware Mapping Report

Overview

This code implements a multi-base calculator for the LPC1768 microcontroller with support for Binary, Octal, Decimal, and Hexadecimal number systems. It features a 4x4 matrix keypad for input, a 16x2 LCD for display, and a single 7-segment display for quick output visualization.

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Core Functionality

1. Number Base Modes

The calculator supports four number bases:

• Binary (BIN) - Base 2 (digits 0-1)
• Octal (OCT) - Base 8 (digits 0-7)
• Decimal (DEC) - Base 10 (digits 0-9) - Default mode
• Hexadecimal (HEX) - Base 16 (digits 0-9, A-F)

Mode switching is done via the P2.12 button in the cycle: DEC → BIN → OCT → HEX → DEC...

2. Keypad Operation

Standard Digit Input (Keys 0-F)

• Keys 0-9 and A-F enter digits
• Only valid digits for the current base are accepted
• Numbers are built up by multiplying the current value by the base and adding the new digit

Operator Mode (Hold Key 0 + Another Key)

The code uses Key 0 as a "shift" key for operator access:

Combination	Function	Operation
Key 0 + B	Addition	Stores current number, sets + operation
Key 0 + C	Clear	Resets all values
Key 0 + D	Subtraction	Stores current number, sets - operation
Key 0 + E	Multiplication	Stores current number, sets × operation
Key 0 + F	Equals	Calculates result based on stored operation

3. Signed Integer Handling

The code uses signed 32-bit integers (int type) with special display logic:

• Decimal mode: Negative numbers shown with "-" sign
• Other bases: Numbers displayed as unsigned (two's complement representation)
• 7-segment display: Decimal point illuminates to indicate negative numbers

4. Display Outputs

LCD Display (16x2)

• Line 1: Current mode ("Mode: BIN/OCT/DEC/HEX")
• Line 2: Input number ("Inp: [number]") or Result ("Res: [number]")
• Brief operator feedback shown when operations are selected

7-Segment Display

• Shows the last digit (rightmost) of the current input in base-16
• Decimal point lights up when the number is negative

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Hardware Mapping to FRC Connectors

CNA Connector (P0.4 to P0.11)

Usage: 7-Segment Display

Pin CNA	LPC1768 Pin	Function	Code Reference
1	P0.4	Segment a	SEG_SHIFT = 4
2	P0.5	Segment b	Bits 4-11 control segments
3	P0.6	Segment c	seven_seg[] array patterns
4	P0.7	Segment d
5	P0.8	Segment e
6	P0.9	Segment f
7	P0.10	Segment g
8	P0.11	Decimal point	Bit 7 of pattern (0x80)
10	GND	Ground

Code Configuration:

#define SEG_SHIFT 4
LPC_GPIO0->FIODIR |= (0xFF << SEG_SHIFT);  // Configure as output
LPC_GPIO0->FIOSET = (seg_pattern << SEG_SHIFT);  // Set segments

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CNB Connector (P1.23-P1.26, P2.10-P2.13)

Usage: 7-Segment Digit Enable & Mode Button

Pin CNB	LPC1768 Pin	Function	Code Reference
1	P1.23	7-Seg Digit Enable	DIGIT_EN (1<<23)
7	P2.12	Mode Button (Input)	MODE_BUTTON (1<<12)
2-6, 8	P1.24-26, P2.10-11, P2.13	Unused
10	GND	Ground

Code Configuration:

#define DIGIT_EN (1<<23)
LPC_GPIO1->FIODIR |= DIGIT_EN;  // P1.23 as output
LPC_GPIO1->FIOSET = DIGIT_EN;   // Enable digit

#define MODE_BUTTON (1<<12)
LPC_GPIO2->FIODIR &= ~MODE_BUTTON;  // P2.12 as input (pull-up)

Mode Button Behavior:

• Active LOW (reads 0 when pressed)
• Debounced with 5-sample stability check
• Cycles through number bases

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CNC Connector (P0.15-P0.22, P2.13)

Usage: 4×4 Matrix Keypad

Pin CNC	LPC1768 Pin	Function	Keypad Role
1	P0.15	Column 0	Output (scan low)
2	P0.16	Column 1	Output (scan low)
3	P0.17	Column 2	Output (scan low)
4	P0.18	Column 3	Output (scan low)
5	P0.19	Row 0	Input (pull-high)
6	P0.20	Row 1	Input (pull-high)
7	P0.21	Row 2	Input (pull-high)
8	P0.22	Row 3	Input (pull-high)
10	GND	Ground

Keypad Matrix Layout:

      Col0  Col1  Col2  Col3
      (15)  (16)  (17)  (18)
Row0 (19)  0    1    2    3
Row1 (20)  4    5    6    7
Row2 (21)  8    9    A    B
Row3 (22)  C    D    E    F

Scanning Algorithm:

1. Set all columns HIGH
2. Pull one column LOW
3. Read row pins
4. If a row is LOW, a key at that (column, row) is pressed
5. Key number = col × 4 + row

Code Configuration:

#define COL_BASE 15
#define ROW_BASE 19
#define COL_MASK (0x0F << COL_BASE)  // P0.15-18
#define ROW_MASK (0x0F << ROW_BASE)  // P0.19-22

LPC_GPIO0->FIODIR |= COL_MASK;   // Columns as output
LPC_GPIO0->FIODIR &= ~ROW_MASK;  // Rows as input

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CND Connector (P0.23-P0.28, P2.0-P2.1)

Usage: 16×2 LCD Display (4-bit mode)

Pin CND	LPC1768 Pin	Function	LCD Pin
1	P0.23	Data bit 4 (D4)	LCD D4
2	P0.24	Data bit 5 (D5)	LCD D5
3	P0.25	Data bit 6 (D6)	LCD D6
4	P0.26	Data bit 7 (D7)	LCD D7
5	P0.27	Register Select (RS)	LCD RS
6	P0.28	Enable (EN)	LCD EN
7-8	P2.0-1	Unused
10	GND	Ground

LCD Communication (4-bit Mode):

• Each byte sent as two 4-bit nibbles (high nibble first)
• RS = 0: Command mode
• RS = 1: Data mode
• EN pulse: Latches data into LCD

Code Configuration:

#define LCD_DATA_SHIFT 23
#define LCD_DATA_MASK (0x0F << LCD_DATA_SHIFT)  // P0.23-26
#define LCD_RS (1<<27)  // P0.27
#define LCD_EN (1<<28)  // P0.28

LPC_GPIO0->FIODIR |= LCD_DATA_MASK | LCD_RS | LCD_EN;  // All outputs

LCD Initialization Sequence:

1. Wait 5ms after power-on
2. Send 0x03 three times (8-bit mode reset)
3. Send 0x02 (switch to 4-bit mode)
4. Configure: 4-bit, 2-line, 5×8 font (0x28)
5. Display ON, cursor OFF (0x0C)
6. Clear display (0x01)
7. Entry mode: increment, no shift (0x06)

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Key Code Functions

Keypad Scanning

unsigned int scan_keypad(void)

• Scans 4×4 matrix by pulling columns low sequentially
• Returns key number (0-15) or 0xFF if no key pressed
• Includes debouncing delay

Shift Key Detection

unsigned int is_key0_pressed(void)

• Specifically checks if Key 0 is being held down
• Enables "operator mode" when Key 0 + another key pressed

Digit Validation

unsigned int is_valid_digit(unsigned int key)

• Ensures entered digit is valid for current base
• BIN: 0-1, OCT: 0-7, DEC: 0-9, HEX: 0-F

LCD Number Display

void lcd_print_num(int num, unsigned int base)

• Handles negative numbers in decimal mode (shows "-")
• For other bases, displays unsigned representation
• Converts number to string in specified base

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Operation Flow Example

Example: Calculate 5 + 3 in Decimal Mode

1. Power on → Mode: DEC, Input: 0
2. Press Key 5 → Input: 5 (displayed on LCD and 7-seg)
3. Hold Key 0 + Press B → "Op: +" feedback, stored = 5, input = 0
4. Press Key 3 → Input: 3
5. Hold Key 0 + Press F → "Res: 8" displayed, input = 8
6. Result can be used for next calculation

Example: Switch to Binary Mode

1. Press P2.12 button → Mode cycles DEC → BIN
2. LCD shows "Mode: BIN"
3. Only keys 0 and 1 are now valid
4. Display shows binary representation

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Debouncing Strategy

Both keypad and mode button use count-based debouncing:

if(key == last_key){
    if(stable < 5) stable++;
}

• Requires 3 consecutive stable reads before acting (stable == 3)
• After action, sets stable = 5 to prevent repeat triggers
• Prevents false triggers from mechanical switch bounce

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Safety & Overflow Handling

if(input_num > 32767) input_num = input_num % 32768;
if(input_num < -32768) input_num = -32768;

• Wraps overflow for signed 32-bit integers
• Prevents display issues with very large numbers

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Pin Configuration Summary Table

GPIO Port	Pins Used	Direction	Function	FRC Connector
P0.4-11	8 bits	Output	7-seg segments	CNA 1-8
P0.15-18	4 bits	Output	Keypad columns	CNC 1-4
P0.19-22	4 bits	Input	Keypad rows	CNC 5-8
P0.23-26	4 bits	Output	LCD data D4-D7	CND 1-4
P0.27	1 bit	Output	LCD RS	CND 5
P0.28	1 bit	Output	LCD EN	CND 6
P1.23	1 bit	Output	7-seg digit enable	CNB 1
P2.12	1 bit	Input	Mode button	CNB 7

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Conclusion

This calculator demonstrates effective use of the LPC1768's GPIO capabilities across multiple peripherals:

• Efficient matrix keypad scanning minimizes pin usage
• 4-bit LCD mode reduces wiring complexity
• Single 7-segment provides instant visual feedback
• Clever "shift key" mechanism provides operator access without dedicated buttons

The hardware mapping efficiently utilizes all four FRC connectors to create a fully functional multi-base calculator with a clean user interface.