Overview

The PIC16F877A is an iconic 8-bit CMOS Flash microcontroller IC manufactured by Microchip Technology. Based on Microchip's 35-instruction RISC architecture, it operates at clock frequencies up to 20 MHz20\text{ MHz} (200 ns200\text{ ns} instruction cycle execution).

Equipped with 8K words (14.3 KB14.3\text{ KB}) of Flash program memory, 368 bytes of RAM, 256 bytes of EEPROM, an 8-channel 10-bit ADC, two Capture/Compare/PWM (CCP) modules, and a universal synchronous/asynchronous serial transceiver (USART), it remains a staple MCU in academic engineering courses, legacy industrial controllers, and hobbyist projects using PICkit programmers.

Quick reference

CPU Core8-bit PIC RISC (Harvard architecture, 35 instructions)
Max Clock Frequency20 MHz20\text{ MHz}
Flash Program Memory8192 words (14.3 KB14.3\text{ KB}, 14-bit word size)
Data RAM368 bytes
Data EEPROM256 bytes
Operating Voltage (VDD)2.0 V to 5.5 V DC (4.5V to 5.5V for 20 MHz)
GPIO Count33 I/O pins (Ports A, B, C, D, E)
ADC Channels8 channels (10-bit resolution)
CCP (PWM) Modules2 independent modules
In-Circuit Serial ProgrammingICSP via RB6 (PGC), RB7 (PGD), and MCLR/VPP
Package40-pin DIP / 44-pin TQFP / 44-pin PLCC

Pinout (DIP-40 Package)

text
                 ┌───┴───┐
     MCLR/VPP  1│ 1   40│ RB7/PGD
      RA0/AN0  2│       │39 RB6/PGC
      RA1/AN1  3│       │38 RB5
      RA2/AN2  4│       │37 RB4
      RA3/AN3  5│       │36 RB3/PGM
     RA4/T0CKI 6│       │35 RB2
      RA5/AN4  7│       │34 RB1
     RE0/RD/AN5 8│PIC16F877A│33 RB0/INT
     RE1/WR/AN6 9│ DIP-40│32 VDD (+5V)
    RE2/CS/AN7 10│       │31 VSS (GND)
           VDD 11│       │30 RD7
           VSS 12│       │29 RD6
     OSC1/CLKIN 13│      │28 RD5
    OSC2/CLKOUT 14│      │27 RD4
      RC0/T1OSO 15│      │26 RC7/RX
      RC1/T1OSI 16│      │25 RC6/TX
      RC2/CCP1 17│       │24 RC5/SDO
      RC3/SCK  18│       │23 RC4/SDI
      RD0      19│       │22 RD3
      RD1      20│       │21 RD2
                 └───────┘

Specifications

ParameterSymbolMinTypMaxUnitConditions
Operating Voltage (20 MHz)VDDV_{DD}4.55.05.5VHS Crystal mode
Operating CurrentIDDI_{DD}—1.63.2mA4 MHz, 5.0V
Standby CurrentIPDI_{PD}—0.15.0µAWDT disabled, 5.0V
Single I/O Pin CurrentIIOI_{IO}-25—+25mAMaximum sink/source
ADC Conversion TimeTADT_{AD}1.6——µsPer 10-bit sample

Programming Connections (PICkit 3 / 4 ICSP Header)

text
  PICkit ICSP Pin                  PIC16F877A DIP-40 Pin
  ┌──────────────┐                ┌──────────────────────┐
  │ 1: VPP / MCLR├───────────────►│ Pin 1: MCLR/VPP      │
  │ 2: VDD (+5V) ├───────────────►│ Pin 11 & 32: VDD     │
  │ 3: VSS (GND) ├───────────────►│ Pin 12 & 31: VSS     │
  │ 4: PGD (Data)├───────────────►│ Pin 40: RB7/PGD      │
  │ 5: PGC (Clock)───────────────►│ Pin 39: RB6/PGC      │
  └──────────────┘                └──────────────────────┘

Common mistakes

  • Leaving MCLR (Pin 1) unpulled or floating: Pin 1 is the Master Clear reset line. If left floating, electromagnetic interference causes random CPU resets. Always pull MCLR up to VDDV_{DD} via a 10 kΩ10\text{ k}\Omega resistor.
  • Forgetting to clear ADCON1 for digital I/O on PORTA: On power-up, PORTA pins default to analog inputs. If reading digital switches on PORTA, registers ADCON1 must be configured (e.g. ADCON1 = 0x06) to switch pins to digital I/O mode.

Notes

  • PIC16F877A vs ATmega328P: PIC16F877A uses 35-instruction 8-bit PIC architecture with 14.3KB Flash in a 40-pin DIP package; ATmega328P uses 131-instruction AVR architecture with 32KB Flash in a 28-pin DIP package.

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