Datasheet

136
6120F–ATARM–03-Oct-06
AT91SAM7X512/256/128 Preliminary
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.
21.4.2 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 21-3 shows a transmission using this protocol.
Figure 21-3. Xmodem Transfer Example
21.4.3 USB Device Port
A 48 MHz USB clock is necessary to use the USB Device port. It has been programmed earlier
in the device 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
C
ACK
SOH 02 FD Data[128] CRC CRC
ACK
SOH 03 FC Data[100] CRC CRC
ACK
EOT
ACK