XMODEM

X-Modem:

Offset            Contents
0                    SOH = Ascii 01
1                    Block #, start with 1, wrap to 0 after FF
2                    Ones complement (XOR with 0xFF) of block #
3-130            128 bytes of data
131                 CRC Checksum of bytes  (carry ignored)

• Delphi (Pascal) code for XMODEM version 16 BIT CRC +

Remember also that the 'window size' is 1. An ASCII ACK must be sent to the sender before the next packet will be sent. If the checksum doesnt match, a NAK must be sent. After 10 NAKs, the transfer should abort. +

Archive:

• PICList post "X-modem protocol" +

See also:

• http://www.geocities.com/westfw/ymodem.txt X / Y MODEM protocol references.+

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