300 lines
9.1 KiB
Markdown
300 lines
9.1 KiB
Markdown
# LPC1768 Multi-Base Calculator - Code Explainer & Hardware Mapping Report
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## Overview
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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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---
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## Core Functionality
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### 1. **Number Base Modes**
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The calculator supports four number bases:
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- **Binary (BIN)** - Base 2 (digits 0-1)
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- **Octal (OCT)** - Base 8 (digits 0-7)
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- **Decimal (DEC)** - Base 10 (digits 0-9) - *Default mode*
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- **Hexadecimal (HEX)** - Base 16 (digits 0-9, A-F)
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Mode switching is done via the **P2.12 button** in the cycle: DEC → BIN → OCT → HEX → DEC...
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### 2. **Keypad Operation**
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#### Standard Digit Input (Keys 0-F)
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- Keys 0-9 and A-F enter digits
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- Only valid digits for the current base are accepted
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- Numbers are built up by multiplying the current value by the base and adding the new digit
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#### Operator Mode (Hold Key 0 + Another Key)
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The code uses **Key 0 as a "shift" key** for operator access:
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| Combination | Function | Operation |
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|-------------|----------|-----------|
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| Key 0 + B | Addition | Stores current number, sets + operation |
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| Key 0 + C | Clear | Resets all values |
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| Key 0 + D | Subtraction | Stores current number, sets - operation |
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| Key 0 + E | Multiplication | Stores current number, sets × operation |
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| Key 0 + F | Equals | Calculates result based on stored operation |
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### 3. **Signed Integer Handling**
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The code uses **signed 32-bit integers** (`int` type) with special display logic:
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- **Decimal mode**: Negative numbers shown with "-" sign
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- **Other bases**: Numbers displayed as unsigned (two's complement representation)
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- **7-segment display**: Decimal point illuminates to indicate negative numbers
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### 4. **Display Outputs**
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#### LCD Display (16x2)
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- **Line 1**: Current mode ("Mode: BIN/OCT/DEC/HEX")
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- **Line 2**: Input number ("Inp: [number]") or Result ("Res: [number]")
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- Brief operator feedback shown when operations are selected
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#### 7-Segment Display
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- Shows the **last digit** (rightmost) of the current input in base-16
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- **Decimal point lights up** when the number is negative
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---
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## Hardware Mapping to FRC Connectors
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### **CNA Connector (P0.4 to P0.11)**
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**Usage: 7-Segment Display**
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| Pin CNA | LPC1768 Pin | Function | Code Reference |
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|---------|-------------|----------|----------------|
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| 1 | P0.4 | Segment a | `SEG_SHIFT = 4` |
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| 2 | P0.5 | Segment b | Bits 4-11 control segments |
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| 3 | P0.6 | Segment c | `seven_seg[]` array patterns |
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| 4 | P0.7 | Segment d | |
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| 5 | P0.8 | Segment e | |
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| 6 | P0.9 | Segment f | |
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| 7 | P0.10 | Segment g | |
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| 8 | P0.11 | Decimal point | Bit 7 of pattern (0x80) |
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| 10 | GND | Ground | |
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**Code Configuration:**
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```c
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#define SEG_SHIFT 4
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LPC_GPIO0->FIODIR |= (0xFF << SEG_SHIFT); // Configure as output
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LPC_GPIO0->FIOSET = (seg_pattern << SEG_SHIFT); // Set segments
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```
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---
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### **CNB Connector (P1.23-P1.26, P2.10-P2.13)**
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**Usage: 7-Segment Digit Enable & Mode Button**
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| Pin CNB | LPC1768 Pin | Function | Code Reference |
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|---------|-------------|----------|----------------|
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| 1 | P1.23 | 7-Seg Digit Enable | `DIGIT_EN (1<<23)` |
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| 7 | P2.12 | Mode Button (Input) | `MODE_BUTTON (1<<12)` |
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| 2-6, 8 | P1.24-26, P2.10-11, P2.13 | *Unused* | |
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| 10 | GND | Ground | |
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**Code Configuration:**
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```c
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#define DIGIT_EN (1<<23)
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LPC_GPIO1->FIODIR |= DIGIT_EN; // P1.23 as output
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LPC_GPIO1->FIOSET = DIGIT_EN; // Enable digit
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#define MODE_BUTTON (1<<12)
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LPC_GPIO2->FIODIR &= ~MODE_BUTTON; // P2.12 as input (pull-up)
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```
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**Mode Button Behavior:**
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- Active LOW (reads 0 when pressed)
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- Debounced with 5-sample stability check
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- Cycles through number bases
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---
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### **CNC Connector (P0.15-P0.22, P2.13)**
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**Usage: 4×4 Matrix Keypad**
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| Pin CNC | LPC1768 Pin | Function | Keypad Role |
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|---------|-------------|----------|-------------|
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| 1 | P0.15 | Column 0 | Output (scan low) |
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| 2 | P0.16 | Column 1 | Output (scan low) |
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| 3 | P0.17 | Column 2 | Output (scan low) |
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| 4 | P0.18 | Column 3 | Output (scan low) |
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| 5 | P0.19 | Row 0 | Input (pull-high) |
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| 6 | P0.20 | Row 1 | Input (pull-high) |
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| 7 | P0.21 | Row 2 | Input (pull-high) |
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| 8 | P0.22 | Row 3 | Input (pull-high) |
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| 10 | GND | Ground | |
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**Keypad Matrix Layout:**
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```
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Col0 Col1 Col2 Col3
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(15) (16) (17) (18)
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Row0 (19) 0 1 2 3
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Row1 (20) 4 5 6 7
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Row2 (21) 8 9 A B
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Row3 (22) C D E F
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```
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**Scanning Algorithm:**
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1. Set all columns HIGH
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2. Pull one column LOW
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3. Read row pins
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4. If a row is LOW, a key at that (column, row) is pressed
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5. Key number = `col × 4 + row`
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**Code Configuration:**
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```c
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#define COL_BASE 15
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#define ROW_BASE 19
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#define COL_MASK (0x0F << COL_BASE) // P0.15-18
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#define ROW_MASK (0x0F << ROW_BASE) // P0.19-22
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LPC_GPIO0->FIODIR |= COL_MASK; // Columns as output
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LPC_GPIO0->FIODIR &= ~ROW_MASK; // Rows as input
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```
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---
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### **CND Connector (P0.23-P0.28, P2.0-P2.1)**
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**Usage: 16×2 LCD Display (4-bit mode)**
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| Pin CND | LPC1768 Pin | Function | LCD Pin |
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|---------|-------------|----------|---------|
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| 1 | P0.23 | Data bit 4 (D4) | LCD D4 |
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| 2 | P0.24 | Data bit 5 (D5) | LCD D5 |
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| 3 | P0.25 | Data bit 6 (D6) | LCD D6 |
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| 4 | P0.26 | Data bit 7 (D7) | LCD D7 |
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| 5 | P0.27 | Register Select (RS) | LCD RS |
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| 6 | P0.28 | Enable (EN) | LCD EN |
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| 7-8 | P2.0-1 | *Unused* | |
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| 10 | GND | Ground | |
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**LCD Communication (4-bit Mode):**
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- Each byte sent as two 4-bit nibbles (high nibble first)
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- **RS = 0**: Command mode
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- **RS = 1**: Data mode
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- **EN pulse**: Latches data into LCD
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**Code Configuration:**
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```c
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#define LCD_DATA_SHIFT 23
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#define LCD_DATA_MASK (0x0F << LCD_DATA_SHIFT) // P0.23-26
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#define LCD_RS (1<<27) // P0.27
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#define LCD_EN (1<<28) // P0.28
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LPC_GPIO0->FIODIR |= LCD_DATA_MASK | LCD_RS | LCD_EN; // All outputs
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```
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**LCD Initialization Sequence:**
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1. Wait 5ms after power-on
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2. Send 0x03 three times (8-bit mode reset)
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3. Send 0x02 (switch to 4-bit mode)
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4. Configure: 4-bit, 2-line, 5×8 font (0x28)
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5. Display ON, cursor OFF (0x0C)
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6. Clear display (0x01)
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7. Entry mode: increment, no shift (0x06)
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---
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## Key Code Functions
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### Keypad Scanning
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```c
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unsigned int scan_keypad(void)
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```
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- Scans 4×4 matrix by pulling columns low sequentially
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- Returns key number (0-15) or 0xFF if no key pressed
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- Includes debouncing delay
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### Shift Key Detection
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```c
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unsigned int is_key0_pressed(void)
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```
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- Specifically checks if Key 0 is being held down
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- Enables "operator mode" when Key 0 + another key pressed
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### Digit Validation
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```c
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unsigned int is_valid_digit(unsigned int key)
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```
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- Ensures entered digit is valid for current base
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- BIN: 0-1, OCT: 0-7, DEC: 0-9, HEX: 0-F
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### LCD Number Display
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```c
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void lcd_print_num(int num, unsigned int base)
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```
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- Handles negative numbers in decimal mode (shows "-")
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- For other bases, displays unsigned representation
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- Converts number to string in specified base
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---
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## Operation Flow Example
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**Example: Calculate 5 + 3 in Decimal Mode**
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1. **Power on** → Mode: DEC, Input: 0
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2. **Press Key 5** → Input: 5 (displayed on LCD and 7-seg)
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3. **Hold Key 0 + Press B** → "Op: +" feedback, stored = 5, input = 0
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4. **Press Key 3** → Input: 3
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5. **Hold Key 0 + Press F** → "Res: 8" displayed, input = 8
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6. Result can be used for next calculation
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**Example: Switch to Binary Mode**
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1. **Press P2.12 button** → Mode cycles DEC → BIN
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2. LCD shows "Mode: BIN"
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3. Only keys 0 and 1 are now valid
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4. Display shows binary representation
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---
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## Debouncing Strategy
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Both keypad and mode button use **count-based debouncing**:
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```c
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if(key == last_key){
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if(stable < 5) stable++;
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}
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```
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- Requires **3 consecutive stable reads** before acting (`stable == 3`)
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- After action, sets `stable = 5` to prevent repeat triggers
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- Prevents false triggers from mechanical switch bounce
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---
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## Safety & Overflow Handling
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```c
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if(input_num > 32767) input_num = input_num % 32768;
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if(input_num < -32768) input_num = -32768;
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```
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- Wraps overflow for signed 32-bit integers
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- Prevents display issues with very large numbers
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---
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## Pin Configuration Summary Table
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| GPIO Port | Pins Used | Direction | Function | FRC Connector |
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|-----------|-----------|-----------|----------|---------------|
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| P0.4-11 | 8 bits | Output | 7-seg segments | **CNA 1-8** |
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| P0.15-18 | 4 bits | Output | Keypad columns | **CNC 1-4** |
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| P0.19-22 | 4 bits | Input | Keypad rows | **CNC 5-8** |
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| P0.23-26 | 4 bits | Output | LCD data D4-D7 | **CND 1-4** |
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| P0.27 | 1 bit | Output | LCD RS | **CND 5** |
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| P0.28 | 1 bit | Output | LCD EN | **CND 6** |
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| P1.23 | 1 bit | Output | 7-seg digit enable | **CNB 1** |
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| P2.12 | 1 bit | Input | Mode button | **CNB 7** |
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---
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## Conclusion
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This calculator demonstrates effective use of the LPC1768's GPIO capabilities across multiple peripherals:
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- Efficient matrix keypad scanning minimizes pin usage
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- 4-bit LCD mode reduces wiring complexity
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- Single 7-segment provides instant visual feedback
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- Clever "shift key" mechanism provides operator access without dedicated buttons
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The hardware mapping efficiently utilizes all four FRC connectors to create a fully functional multi-base calculator with a clean user interface.
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