usart.asm

2021/05/30 2021/12/20

This program provides basic USART routines. This code is a part of pAVRlib.

In examples/ you'll find a small test program.

The software UART is written based on Application Note AVR305.

Initialize

Before you use this routines, you need define F_CPU (in Hz) and USART_BAUD.

.equ F_CPU = 1000000
.equ USART_BAUD = 4800

Furthermore you need to define the ports if you use AVR without a hardware USART (e.g. ATtiny25).

; PB3 and PB4 (Pin 2 and 3 of ATtiny25/45/85)
.equ USART_DDR  = DDRB
.equ USART_PORT = PORTB
.equ USART_PIN  = PINB
.equ USART_RXD  = 3
.equ USART_TXD  = 4

Subroutines

`void USART_INITIALIZE()` (in: (none), out: (none))

set up the port and baudrate.

`void USART_TRANSMIT(char)` (in: r24, out: (none))

send a byte.

`char USART_RECEIVE()` (in: (none), out: r24)

receive a byte.

Example

This is a simple echo program.

	rcall	USART_INITIALIZE
loop:
	rcall	USART_RECEIVE
	rcall	USART_TRANSMIT
	rjmp	loop