🖧 PIC16F57 LCD Display – Binary and Decimal Counter

by Lewis Loflin

This page cover using and setting up the PIC16F57. It is very basic, inexpensive, and great for testing hardware. Hardware is the focus here.

The next project in the link below uses the PIC16F57 microcontroller to count from 0 to 255, displaying both the binary and decimal values on an HD44780-compatible LCD. The counter updates every 500 milliseconds using TMR0 driven by an external 60 Hz timebase. It’s a straightforward hardware test designed to verify the PIC16F57's function, explore its quirks (such as the 2-level call stack), and demonstrate practical embedded development — with no simulation software involved.

Every aspect of this circuit is tested on real hardware. No guesses, no virtual models — just measurable, observable behavior. This is not a sandbox — it’s a lab.

See 8-Bit LCD Interface with PIC16F57: Binary and Decimal Counter in C (XC8)

The PIC16F57 is perfect for testing eight-bit hardware and that is the focus with these projects.

⚠️ Why I Don't Use Simulation Software

Many visitors to this site attempt to simulate these circuits using SPICE-based tools or drag-and-drop simulators — and then wonder why they don’t work. Here's the reality:

• I don’t use simulation software. Every circuit here is built and tested with real components on real hardware.
• I use what I have. Most of these designs came from years of doing electronics with limited resources, salvaged parts, and creative workarounds.
• Simulators can’t model non-conventional solutions. They don’t account for the quirks, timing delays, or logic tricks that real-world hardware reveals — especially when using components outside their typical applications.

If you're serious about learning how electronics actually work — build it, measure it, break it, and fix it. That’s what I do here.

This isn’t a sandbox. It’s a lab.

⚠️ Real Hardware Matters: The 2-Level Stack Problem

A perfect example of why simulation isn’t enough: the PIC16F57 has a fixed two-level return stack. That means it can only remember the return addresses for two nested subroutine calls.

See PIC16F57 Serial LCD and 4x4 Keypad Demo

This isn’t just a technical detail — it can cause program crashes, missed returns, or corrupt behavior if you nest more than two calls. And the worst part?

I would never have spotted this unless I actually ran a program and debugged it. The simulator didn’t show it — the hardware did.

If you're using chips like the 16F57, you must test on real hardware to find these hidden limitations. Simulators won't show stack overflows, pin conflicts, or timing glitches — only live debugging will.

Test it. Watch it fail. Learn why — and fix it.

Characteristics of Microchip PIC16F57, PIC16F84A, PIC16F628A, PIC12F683, PIC16F690.
Click image for larger view.

What works on the PIC16F57

• PIC16F57 projects.
• PIC16F57 using TMR0 with External 60Hz or 120Hz Clock
• 8-Bit LCD Interface with PIC16F57: Binary and Decimal Counter in C (XC8)
• PIC16F57 Serial LCD and 4x4 Keypad Demo
• Simulate PLC Ladder Logic with PIC16F57 Microcontroller – Simple C Example

📘 PIC16F57 Register File Map

⁽¹⁾INDF is not a physical register; it is used with FSR for indirect addressing.

Note 1: INDF is not a physical register. See Section 3.7, "Indirect Data Addressing; INDF and FSR Registers."

📌 Special Instruction Notes:

• TRIS (Tri-State): TRISA, TRISB, and TRISC are not real file registers. They are accessed via instructions such as:

  CLRF PORTB        ; Clear PORTB
  MOVLW 0x00        
  TRIS PORTB        ; Set all PORTB pins as output
  
  CLRF PORTC
  TRIS PORTC        ; Set all PORTC pins as output
  
  CLRF PORTA
  MOVLW 0x0F
  TRIS PORTA        ; Set lower 4 bits of PORTA as input (RA0–RA3)
    

  These configure I/O direction but do not occupy memory addresses. This is why they do not appear in the register file map.
• OPTION: Like TRIS, the OPTION register is not memory-mapped. It is configured using the OPTION instruction (or OPTION_REG in newer PICs). This sets up the prescaler, TMR0 edge, but has no direct file address.
• TMR0: Although TMR0 appears at address 01h, it is both readable and writable. It is used in conjunction with the OPTION instruction to configure prescaler settings and clock source. TMR0 overflows can not trigger interrupts PIC16F84A, PIC16F128A, etc., no interrupts exist in the PIC16F57.

🛠️ Best Practice: Clear All PORTs Before Use

In all of my assembly programs, I make it a rule to clear PORTA, PORTB, and PORTC during initialization — even if they are not used.

This avoids potential problems caused by unpredictable startup states or leftover values from resets. Uninitialized ports may float, latch, or output spurious logic levels, which can interfere with proper operation or downstream hardware.

CLRF PORTA
CLRF PORTB
CLRF PORTC
  

Note: This is especially important on older devices like the PIC16F54 or PIC16F57, where all ports are digital and have no analog fallback or default behavior.

PIC16F57 Intro Project: 8-bit Binary Counter

by Lewis Loflin

See PIC16F57 wiring connections.

This project uses the PIC16F57 to generate a binary count (0–255) on PORTC, updating every 500 milliseconds. This is a basic test to confirm that the microcontroller, crystal oscillator, and PORTC outputs are functioning properly.

PIC16F57 Characteristics and Observations

• Mid-range 8-bit microcontroller with Harvard architecture
• No hardware stack pointer—only 2-level hardware call stack
• No interrupts, no ADC, no EEPROM, no UART
• One 8-bit timer (TMR0) with external input; no overflow flag
• Simple instruction set, ideal for 8-bit digital logic testing
• Great for driving parallel devices like LCDs or LED matrices
• Limited for complex C programs—only two nested function calls allowed
• Encourages “flag-based” logic similar to PLC programming
• Ideal for experimenting with 4×4 keypads, shift registers, etc.

See Zero-Crossing Detectors Circuits and Applications

See Improved AC Zero Crossing Detectors for Arduino

T0CLKI (pin 1) is the TMR0 external clock input. It has a Schmitt trigger input. Must be tied to VSS or VDD, if not in use, to reduce current consumption.

T0CKI (pin 1) is Schmitt Trigger clock input to Timer0. Must be tied to VSS or VDD, if not in use, to reduce current consumption.

Two level hardware stack, operating voltage 2V - 5.5V.

Hardware Setup

• Microcontroller: PIC16F57
• Oscillator: 4 MHz external crystal
• PORTC: Connected to 8 LEDs through 220Ω resistors
• TRISA: Lower 4 bits set as input (future use)
• TRISB: Set as input, not used in this example

Test Code

// 8 LEDs on PORTC
// PIC16F57 C Version: Count 0–255 (binary) on PORTC with 500ms delay
// Assumes external 4 MHz crystal
// 51 bytes program 12 bytes SRAM with MPLAB X and C8.

#include <xc.h>
// Configuration bits
#pragma config WDT = OFF   // Watchdog Timer disabled
#pragma config CP = OFF     // Code protection off
#pragma config OSC = XT    // XT Oscillator (use 4 MHz crystal)

#define _XTAL_FREQ 4000000UL

void INIT57(void)   {
    // TRIS settings
    // TRISA = 0x0F; // Lower 4 bits as input, upper bits output
    // TRISB = 0xFF; // All input
    TRISC = 0x00; // All output 
    
    // Clear all ports
    PORTA = 0x00; 
    PORTB = 0x00;   
    PORTC = 0x00;    
}

void main(void) {
    INIT57();
    unsigned char counter = 0;
    while (1) {
        PORTC = counter;
         __delay_ms(500);
        counter++;
    }
}

This example uses only 8 output pins and very little flash or SRAM. It’s ideal as a first test when evaluating a PIC16F57 for 8-bit digital output applications.

Click for schematic | Visit Hobby Page

🔄 Comparing PORTB Pull-Ups and Interrupts: PIC16F84A vs. PIC16F628A

✅ Common Features

• RB0/INT: Both chips support external interrupt-on-change on RB0 (INT pin), triggered on rising or falling edge depending on configuration.
• RB4–RB7 Interrupt-on-Change: Both support interrupt-on-change on RB4–RB7 when any of these bits change state.
• PORTB Pull-Ups: Both offer weak internal pull-ups on RB0–RB7 when enabled.

Differences

🧠 Additional Notes

• The PIC16F628A is code-compatible with the 16F84A in most I/O applications.
• Internal pull-ups are weak (~20–50kΩ); use external resistors if stronger bias is needed.
• Interrupt-on-change only detects logic level transitions, not edges.

• The next two pages focuses on Timer0 and interrupts in the PIC16F84A.
• PIC16F84A – TMR0 with External 60Hz Timebase on RA4 (Pin 3)
• PIC16F84A Interrupt Examples – RB0 and RB4–RB6 with LED Toggling
• Comparing PORTB Pull-Ups and Interrupts: PIC16F84A vs. PIC16F628A

• Using Timer1 on the PIC16F628A as a Pulse and Frequency Counter
• PIC16F628A Interrupt-on-Change Debounced Button Input on RB4
• PIC16F628A – Interrupt-Driven 1Hz Square Wave from 60Hz Input
• Using a 32.768 kHz Crystal with Timer1 on the PIC16F628A
• Interfacing HD44780 LCD with PIC16F628A in 4-Bit Mode
• PIC16F628A: Displaying Decimal Numbers on LCD 4-Bit Mode
• PIC16F628A PWM Output with Fade Example – 1 kHz LED Control

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Common register control using C-style bitwise logic:

These are especially useful when working with individual I/O pins without affecting other bits in a register.

#pragma config Overview

#pragma is used to send special instructions to the compiler. In XC8, it's mainly used to set configuration bits (fuses) directly from your C source code.

These lines are essential for ensuring your microcontroller starts up with the correct hardware settings. Without them, you'll rely on manual IDE configuration — and that can lead to mismatched builds.

#define bitset(var, bitno)   ((var) |=  (1 << (bitno)))   // Set bit
#define bitclr(var, bitno)   ((var) &= ~(1 << (bitno)))   // Clear bit
#define bitflip(var, bitno)  ((var) ^=  (1 << (bitno)))   // Toggle bit
#define bitcheck(var, bitno) (((var) &   (1 << (bitno))) != 0)  // Check bit
  

🕒 Using _XTAL_FREQ and Delay Macros in XC8

To use __delay_ms() and __delay_us() in MPLAB XC8 projects, you must define the system clock frequency using _XTAL_FREQ as an unsigned long.

✅ Example Setup

#include <xc.h>
  
// Configuration bits
#pragma config WDT = OFF   // Watchdog Timer disabled
#pragma config CP = OFF     // Code protection off
#pragma config OSC = XT    // XT Oscillator (use 4 MHz crystal)

#define _XTAL_FREQ 4000000UL  // Required: 4 MHz crystal, note the UL!

void main(void) {
    TRISB = 0x00;      // PORTB output
    PORTB = 0x00;

    while (1) {
        PORTB ^= 0x01;  // Toggle RB0
        __delay_ms(500);  // 500ms delay
    }
}

📌 Key Notes

• _XTAL_FREQ must be defined before any __delay_xx() macros are used.
• Always use the UL suffix (e.g., 4000000UL) to ensure correct arithmetic.
• __delay_ms(x) and __delay_us(x) are built-in macros, not functions.
• They do not stop interrupts and should be avoided inside ISRs.
• They expand into inline delay loops based on the defined frequency.

🚫 Common Pitfalls

• Missing UL → Wrong delay or compiler errors
• Defining _XTAL_FREQ after delay use → fails silently
• Using delays with optimization on → may be reduced or eliminated

🔧 Flash Usage Comparison – Toggling RB1 on PIC16F57

Compiled with XC8 for PIC16F57, these code snippets toggle LED on RB1. Measured flash usage illustrates macro efficiency:

Macro used:

#define bitflip(var, bitno) ((var) ^= (1 && (bitno)))

Conclusion: For size-critical code, direct macros like bitflip() save valuable flash on baseline PICs such as the 16F57.

🔍 Understanding int8_t and int16_t in Embedded C

The types int8_t and int16_t are part of the <stdint.h> header and define fixed-width signed integers. These are essential in embedded systems where memory and data width must be tightly controlled.

📘 Why Use These Types?

• Guarantees the exact size of variables regardless of compiler or architecture
• Avoids overflow or data truncation issues
• Ideal for I/O registers, binary sensors, and precise data formats like temperature readings

🌡️ Example: DS18B20 Temperature Reading

The DS18B20 sensor returns a 16-bit signed value that must be interpreted correctly. This is why we use:

int16_t temp;     // Holds raw 16-bit signed temperature from DS18B20
int8_t whole;     // Stores the integer (whole °C) part of the temperature
uint8_t frac;     // Stores the fractional part (in tenths of a degree)

For example, if the sensor returns 0x00A2, that equals 162 / 16 = 10.125°C. The code separates this into:

• whole = 10
• frac = 1 (tenths of a degree)

Using these types ensures accurate, portable temperature display on an LCD or serial output.