Pic Serial Communication Assembly Code

How to Implement Serial Communication with PIC Microcontrollers using Assembly Code

Serial communication is a common way of transferring data between devices using a serial bus. It involves sending data one bit at a time, sequentially, over a single wire or pair of wires. Serial communication can be either synchronous or asynchronous, depending on whether the sender and receiver share a common clock signal or not.

PIC microcontrollers have a built-in module called EUSART (Enhanced Universal Synchronous Asynchronous Receiver Transmitter) that can be used to implement serial communication with other devices. The EUSART module can operate in different modes, such as 8-bit or 9-bit transmission, synchronous or asynchronous mode, full-duplex or half-duplex mode, etc. The EUSART module can also generate and detect start bits, stop bits, parity bits, and framing errors.

In this article, we will show how to write assembly code to configure and use the EUSART module of PIC microcontrollers for serial communication. We will use PIC16F877A as an example, but the code can be adapted for other PIC microcontrollers with similar EUSART modules. We will assume that the PIC microcontroller is running at 4 MHz using an external crystal oscillator.

We will create two programs: one for the transmitter and one for the receiver. The transmitter will send a string of characters \"Hello World!\" to the receiver over the serial bus. The receiver will display the received characters on an LCD module. We will use a USB-TTL converter or an FTDI chip to connect the PIC microcontroller to a PC for debugging purposes.

The following circuit diagram shows the connections between the PIC microcontroller, the USB-TTL converter, and the LCD module:

The following table shows the pin assignments for the PIC microcontroller:

PIC PinFunctionConnection

RA0RS (LCD)Pin 4 of LCD

RA1RW (LCD)Pin 5 of LCD

RA2E (LCD)Pin 6 of LCD

RB0-RB3Data (LCD)Pins 11-14 of LCD

RC6/TXTransmit (EUSART)RX pin of USB-TTL converter

RC7/RXReceive (EUSART)TX pin of USB-TTL converter

VDD+5V Power Supply+5V pin of USB-TTL converter and Pin 2 of LCD

VSSGND Power SupplyGND pin of USB-TTL converter and Pin 1 of LCD

MCLRReset Pin+5V through a 10k resistor

OSC1/CLKINClock Input4 MHz crystal oscillator with two 22pF capacitors to GND

OSC2/CLKOUTClock Output4 MHz crystal oscillator with two 22pF capacitors to GND

The following code shows the assembly program for the transmitter:

```

; Define constants

#define _XTAL_FREQ 4000000 ; Oscillator frequency

#define BAUDRATE 9600 ; Baud rate for serial communication

#define SPBRG_VALUE ((_XTAL_FREQ/BAUDRATE)/64)-1 ; Value for SPBRG register

; Define variables

DATA EQU 0x20 ; Data buffer

MSG EQU 0x21 ; Message pointer

STR EQU 0x22 ; String to send

; Initialize 061ffe29dd