xAppSoftware

Using the Standard IO facilities of the avr-libc 

The avr-libc gives some facilities of the standard I/O. Only a limited subset of the standard IO is implemented (refer to the <stdio.h>: Standard IO facilities section of the avr-libc manual.). The uart.c source code could be used to interface the uart device with the Standard IO. The following example from the stdio man page of avr-libc illustrates the usage of the uart library.

Frame format

The frame formats supported by the Atmega is the standard UART frame format, specifically it accepts all 30 combinations of the following as valid frame formats:

 1 start bit

 5, 6, 7, 8, or 9 data bits

 no, even or odd parity bit

Transmission

The USART Transmitter is enabled setting the Transmit Enable (TXEN) bit in the UCSR0B Register. When the Transmitter is enabled, the normal port operation of the TxD0 pin is overridden by the USART and given the function as the Transmitter’s serial output. 

USART in Atmel AVR (ATMEGA88 and ATMEGA328P)

The main features of the USART module in the AVR micro controller are:

1.Full Duplex Operation with Independent Serial Receive and Transmit Registers

2.Asynchronous or Synchronous Operation

3.Master or Slave Clocked Synchronous Operation

4.High Resolution Baud Rate Generator

Connectors

There are a lot of connectors type for rs232 interfaces, in the table RS232 Connectors we show the most used connectors:

Connector	Male	Female
DB25
DB9
RJ45
DB8 mini DIN

Bits, Baud and Symbols

Baud is a measurement of transmission speed in asynchronous communication. Because of advances in modem communication technology, this term is frequently misused when describing the data rates in newer devices.

The RS232-C and V.24 Standards

In most computer systems, the UART is connected to circuitry that generates signals that comply with the EIA (Electronics Industry Association) RS232-C  (Recommend Standard  number 232 revision C) specification (there is also a CCITT standard named V.24 that mirrors the specifications included in RS232-C). The RS232-C defines the electrical specifications of the serial port; the signals are represented by voltage levels with respect to a common signal ground.

The Usart Bla bla bla
A little disquisition about USART and AVR microcontroller

The Usart Bla bla bla
A little disquisition about USART and AVR microcontroller

The scope of this serie of articles is to explain the USART in depth and its use with the microcontroller AVR.

A new article will be published each week.

The MC9RS08KA1 & MC9RS08KA2 watchdog timer.

The watchdog timer (Freescale named it COP Computer Operate Properly)can only cause the System Reset of the device and it has not the interrupt generation capability.