SAM7S161_14 Datasheet, PDF (147/775 Pages) ATMEL Corporation – ARM-based Flash MCU

21.5.1 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.
21.5.2 Xmodem Protocol
The Xmodem protocol supported is the 128-byte length block. This protocol uses a two-character CRC-16 to guar-
antee 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 21-4 shows a transmission using this protocol.
Figure 21-4. Xmodem Transfer Example
Host
Device
C
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
21.5.3 USB Device Port
A 48 MHz USB clock is necessary to use the USB Device port. It has been programmed earlier in the device initial-
ization procedure with PLLB configuration.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
147