User guide

Atmel AVR2054: Serial Bootloader User Guide [APPLICATION NOTE]
8390D−WIRELESS−03/2015
8
Table 2-1. Default COM port settings for embedded bootloader host
Baud rate
38400
Data bits
8
Parity
None
Stop bits
1
Flow control
None
For Atmel PC Bootloader tool to operate correctly as a host over UART it shall get the connection enumerated as a COM
port and configured as described in Table 2-1.
2.1.2 USB-FIFO interface
USB-FIFO interface is a special connection to a PC via USB cable on the Sensor Terminal Board [9].
It requires installation of
ThirdPartySoftware\USB_FIFO_FTDI_Driver\ driver on the PC to get the connection
enumerated as a COM port. Bootloader PC tool shall use COM port settings given in Table 2-1.
This interface is not recommended for reuse on custom boards.
2.1.3 TWI interface
When TWI interface is used the embedded bootstrap operates MCU in TWI slave mode with TWI slave bus address
equal 0x55.
Caution: TWI interface in the embedded bootloader must be used only alone and cannot be enabled together with any
other serial interface.
When using Bootloader PC tool it is recommended to have Xmega-A1 Xplained board [13] as a TWI-to-USB bridge that
provides connection to the PC and can get it enumerated as a COM port.
Atmel XMEGA-A1 Xplained kit contains ATxmega128A1 and AT32UC3B1256 devices. The preprogrammed
AT32UC3B1256 device acts as a USB-to-UART gateway. The ATxmega128A1 device on this board shall be
programmed with the firmware image ‘XplainedA1SerialToI2CBootLoaderBridge.hex’ from
\ThirdPartySoftware\XMEGA_A1_Xplained_Firmware\ to make it act as a USART-to-TWI bridge. TWI on PORTD
is used by ATxmega128A1 and thus GPIO0 (SDA) and GPIO1 (SCL) of PORTD of XMEGA PORTD header of Xplained
board shall be used to connect to the target MCU via TWI. The programming of firmware image to ATxmega128A1
device is explained in “Connecting the board” Section of AVR1927: XMEGA-A1 Xplained Getting Started Guide [12].
When connecting the XMEGA-A1 Xplained to PC, the operating system will request a driver file for installing the serial
communication driver. This driver file ‘XPLAINED_Virtual_Com_Port.inf’ is available in
\ThirdPartySoftware\XMEGA_A1_Xplained_Firmware\ folder.
After VCP has enumerated PC Bootloader tool should be used with COM port settings given in Table 2-1.
2.2 Fuse bits settings
This section does not consider SAM3S and SAMR21 because they do not have fuse bits.
An MCU must be aware of the size of the memory occupied by the bootloader if it resides in the flash and must start from
the bootloader section rather than from the application section.
Recommended fuse bits for supported AVR
®
microcontrollers are given in Table 2-2 and fuse bits for supported XMEGA
®
microcontrollers are given in Table 2-3. The tables list all fuse bits and show the resulting fuse bytes as well.