File Transfer Utilities; Xmodem - Solectek skyway series User Manual

File Transfer Utilities

112
At times it is necessary to upgrade the SkyWay Bridge/Router software. You can do this
remotely using the file transfer utilities, Xmodem, Ymodem, or TFTP . Typically you will
need to upgrade the Runtime Application with a new release of the software.
The three file transfer utilities are Xmodem, Ymodem, and TFTP .

Xmodem

Xmodem is a file transfer protocol with the following ASCII character definitions:
<SOH>
<EOT>
<ACK>
<NAK>
<CAN>
Xmodem is a receiver-driven, asynchronous, 8 data bit protocol. Each packet has the
following format:
<SOH> <packet>
where:
<packet>
<compliment #>
<checksum>
When the receiver is ready, it sends a NAK every 10 seconds (up to one minute) until
the transmitter acknowledges the NAK by sending the first packet. The transmitter
continues by sending each packet in turn, always waiting for the packet to be acknowl-
01H This is always the first byte in
each block.
04H This is sent instead of SOH to
mark the end of transmission.
06H Positive Acknowledgement.
15H Negative Acknowledgement
18H Cancel transfer.
<compliment #>
<SOH> = 01H
= Packet number, starting at 01, incre-
menting by 1, and wrapping from
0FFH to 00H (not 01H)
= 255 minus the packet number
<data> = 128 bytes of binary data
= The sum of the data bytes. Starting
with zero, add each data byte to the
checksum and use only the rightmost
8 bits.
<data> <checksum>