ATMEL AVR1510 User Manual
http://www.BDTIC.com/ATMEL
AVR1510: Xplain training - XMEGA USART
Prerequisites
• Required knowledge
AVR1500: Xplain training – XMEGA™ Basics
AVR1502: Xplain training – XMEGA Direct Memory Access Controller
• Software prerequisites
Atmel
WinAVR/GCC 20100110 or later
• Hardware prerequisites
Xplain evaluation board
JTAGICE mkII
• Estimated completion time:
1.5 hours
1 Introduction
The USART (Universal Synchronous Asynchronous Receiver Transmitter) is the
key element in serial communications between computers, terminals and other
devices.
This training covers basic setup and use of the Atmel XMEGA USART and the
three tasks will demonstrate how to use the USART I polling-mode, interrupt mode
and how to use the DMAC (Direct Memory Access Controller) to transfer data
without CPU interaction.
®
AVR® Studio® 4.18 or later
8-bit
Microcontrollers
Application Note
Rev. 8319A-AVR-06/10
2 Overview
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This training covers some of the Atmel XMEGA USART basic features:
Task 1: Polled mode
The first task shows how to set up the USART in polling mode. Some characters will
be transferred in loop-back mode.
Task 2: Interrupt mode
This task shows how to use a driver to set up the USART. The driver has a ring buffer
that makes life easier for the developer. Also the hardware buffer is shown in this
task.
Task 3: DMAC
Atmel XMEGA introduces Direct Memory Access Controller (DMAC) for 8-bit
processors. With the USART, DMAC is very useful allowing data to flow with nearly
no CPU intervention. This task will show how to set up the USART with the DMAC.
2
AVR1510
8319A-AVR-06/10
3 Task 1: USART in polling mode
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Using polling mode with the USART is especially useful when for example debugging
the application or when steps in the program are expected to happen synchronously.
In this task, we will set up the Xplain evaluation board to send data from USART to
another USART. This is a good way to test the USART.
The goal for this task is that you know how to:
• Set up the USART in polling mode
• Send some characters in loop-back mode
• Verify that the transmission was successful
1. Start Atmel AVR Studio and open the project file Polled_Usart.aps in the XMEGAUSART folder
2. On the Xplain evaluation board, connect a jumper or cable between pins PD2 and
PD3
AVR1510
3.1 Baud rate
The Baud rate is calculated by using the peripheral frequency (f
BSEL as parameters. The target frequency and peripheral frequency on the Atmel
XMEGA is set to 2 MHz default. The BSEL bits are setting the baud rate, and the
BSCALE is adding even more functionality, but is ignored at this stage. By setting
BSCALE to 0, the BSEL can be found by Equation 3-1.
-
Equation 3
BSEL
3. Calculate and find the BSEL value for f
4. Verify that the calculated value is the same as in task1.c
5. Compile the project and verify that there are no errors or warnings
1. Equation for Calculating BSEL Value
f
BSCALE
PER
162
⋅
f
BAUD
=
1
−
BAUD
= 9600
), the BSCALE and
PER
8319A-AVR-06/10
3
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