AT91SAM9G20 datasheet(83/832 Pages) ATMEL

83 / 832 page

6384D–ATARM–04-May-09

AT91SAM9G20 Preliminary

13.10.1

DBGU Serial Port

Communication is performed through the DBGU serial port initialized to 115200 Baud, 8, n, 1.

The Send and Receive File commands use the Xmodem protocol to communicate. Any terminal

performing this protocol can be used to send the application file to the target. The size of 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.

13.10.2

Xmodem Protocol

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

ter 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 13-8 shows a transmission using this protocol.

Figure 13-8. Xmodem Transfer Example

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

AT91SAM9G20 Datasheet(PDF) 83 Page - ATMEL Corporation