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The popular 16F877A.

The 16F877A is one of the most popular PIC microcontrollers and it's easy to see why - it comes in a 40 pin DIP pinout and it has many internal peripherals.

The only disadvantage that you could level at it is that it does not have an internal clock source like most of the other more modern PIC's. However using an external clock usually results in faster operation since you can select a 20MHz crystal instead of the usual internal 8MHz oscillator.

The 16F877A is a capable microcontroller that can do many tasks because it has a large enough programming memory (large in terms of sensor and control projects) 8k words and 368 Bytes of RAM. This is enough to do many different projects (see links at end of this page for some example projects on this site).

Note: There is a more modern part (the 16F887) that has nearly the same functionality as the 16F877A but also includes an internal clock - like the 16F88 and the 18F4550. In addition the 16F887 also has low power operation using nano watt^TM technology.

Differences Between 16F877A and 16F887

Interface	16F877A	16F887	Description
RA4/T0CKI	Open drain	Normal CMOS	The pin is physically different so the input characteristics are changed.
Cost	Expensive	Cheaper	Modern devices are usually cheaper.
ADC	Yes	More useful	More controls although different registers are used.
Nano Watt^TM	No	Yes	16F88x - ultra low power operation (battery operation).
Internal Clock	No	Yes	8Mhz to 31kHz 1% accuracy.
External Gate	No	Yes	External Timer1 gate input (start Timer1 counter).
Volt reference	No	Yes	Internal 0.6V voltage reference.
RS485, LIN 2.0	No	Yes	Enhanced USART supports RS485 and LIN 2.0 operation.
Parallel Slave port	Yes	No	Acts as an 8 -bit processor interface i.e. another 8 bit processor can read and write to this interface controlling the 16F877A as a slave processor.

The four features that you might make you use a 16F887 instead of a 16F877(A) are

External gate.
Volt Reference.
Nano Watt^TM.
Internal Clock.

The gate could be used to more accurately capture an input time e.g. for a reciprocal frequency counter.

The volt reference means you don't need an external reference although it will probably not be useful for highly accurate operation. It is definitely more useful in a battery powered operation where you want to compare the input battery voltage to a known reference e.g. using the comparator and the internal 0.6V reference.

Nano Watt^TM could be useful for battery powered operation.

The internal clock is useful for lab development (not for accuracy) and for general operation - it can also be set to 31kHz so consuming less power.

All the above depend on your specific application requirements.

16F877A

The 40 pins make it easier to use the peripherals as the functions are spread out over the pins. This makes it easier to decide what external devices to attach without worrying too much if there are enough pins to do the job.

One of the main advantages is that each pin is only shared between two or three functions so its easier to decide what the pin function (other devices have up to 5 functions for a pin).

A slight disadvantage of the device is that it has no internal oscillator so you will need an external crystal or other clock source. However the internal oscillator is only 1% accurate and adding a crystal (max 20MHz crystal - for 5MHz internal instruction cycle) and two 15pF capacitors is not a great chore - the accuracy will be 100ppm depending on the crystal used.

Pinout

The pinout of the 16F877A is:

Internal Peripherals

As you can see the chip is full of peripherals so you can use it for many different projects.

The main peripherals of the 16F877A are:

2 CCP modules Capture Compare PWM (select one of three operations).
2 Analogue comparators.
A Serial interface (either I2C or SPI operation).
A USART Universal Synchronous Asynchronous Transmitter Receiver (Rs232 interface).
3 Timers.
1 ADC Analogue to Digital Converter with multiplexor for 10 inputs.
33 I/O pins.
8192 Program words of re-programmable FLASH memory.
368 Bytes of RAM.
256 Bytes of EEPROM.
A Parallel Slave Port.

As you can see the device has a rich set of internal peripherals that can be used for many different designs.

The most unusual internal peripheral is the parallel Slave Port (PSP) and this makes the device compatible with an 8 bit bus so you can directly interface the 16F877A into a system that uses an 8 bit bus. Although this is probably not common now you could enhance an existing system by adding this device i.e. enhance by adding the capabilities of all the other internal peripherals.

More 16F877/A Projects:

8 Digit 7 Segment
Frequency Counter