AT91SAM9261 datasheet(91/688 Pages) ATMEL

91 / 688 page

6062F–ATARM–05-Dec-06

AT91SAM9261 Preliminary

the binary file to send depends on the SRAM size embedded in the product. In all cases, the

size of the binary file must be lower than the SRAM size because the Xmodem protocol

requires some SRAM memory to work.

13.5.2

Xmodem Protocol

The Xmodem protocol supported is the 128-byte length block. This protocol uses a two-char-

acter CRC-16 to guarantee detection of a maximum bit error.

Xmodem protocol with CRC is accurate provided both sender and receiver report successful

transmission. Each block of the transfer looks like:

<SOH><blk #><255-blk #><--128 data bytes--><checksum> in which:

– <SOH> = 01 hex

– <blk #> = binary number, starts at 01, increments by 1, and wraps 0FFH to 00H

(not to 01)

– <255-blk #> = 1’s complement of the blk#.

– <checksum> = 2 bytes CRC16

Figure 13-7 shows a transmission using this protocol.

Figure 13-7. Xmodem Transfer Example

13.5.3

USB Device Port

A 48 MHz USB clock is necessary to use the USB Device port. It has been programmed ear-

lier in the device initialization procedure with PLLB configuration.

The device uses the USB communication device class (CDC) drivers to take advantage of the

installed PC RS-232 software to talk over the USB. The CDC class is implemented in all

releases of Windows®, from Windows 98SE to Windows XP. The CDC document, available at

www.usb.org, describes a way to implement devices such as ISDN modems and virtual COM

ports.

Host

Device

SOH 01 FE Data[128] CRC CRC

ACK

SOH 02 FD Data[128] CRC CRC

ACK

SOH 03 FC Data[100] CRC CRC

ACK

EOT

ACK

AT91SAM9261 Datasheet(PDF) 91 Page - ATMEL Corporation