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I think its time for me to
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(1) document it; (people call me and say "my product is going to include
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it - what can I 'reference'", or "I'm writing a paper on it, what do I put
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in the bibliography") and
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(2) propose an "incremental extension" to it, which might take "exactly"
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the form of Chuck Forsberg's YAM protocol. He wrote YAM in C for CP/M and
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put it in the public domain, and wrote a batch protocol for Unix[4] called
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rb and sb (receive batch, send batch), which was basically XMODEM with
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(a) a record 0 containing filename date time and size
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(b) a 1K block size option
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(c) CRC-16.
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He did some clever programming to detect false ACK or EOT, but basically
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left them the same.
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People who suggest I make SIGNIFICANT changes to the protocol, such as
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"full duplex", "multiple outstanding blocks", "multiple destinations", etc
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etc don't understand that the incredible simplicity of the protocol is one
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of the reasons it survived to this day in as many machines and programs as
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it may be found in!
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Consider the PC-NET group back in '77 or so - documenting to beat the band
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- THEY had a protocol, but it was "extremely complex", because it tried to
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be "all things to all people" - i.e. send binary files on a 7-bit system,
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etc. I was not that "benevolent". I (emphasize > I < ) had an 8-bit UART,
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so "my protocol was an 8-bit protocol", and I would just say "sorry" to
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people who were held back by 7-bit limitations. ...
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Block size: Chuck Forsberg created an extension of my protocol, called
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YAM, which is also supported via his public domain programs for UNIX
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called rb and sb - receive batch and send batch. They cleverly send a
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"block 0" which contains the filename, date, time, and size.
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Unfortunately, its UNIX style, and is a bit weird[5] - octal numbers, etc.
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BUT, it is a nice way to overcome the kludgy "echo the chars of the name"
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introduced with MODEM7. Further, chuck uses CRC-16 and optional 1K
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blocks. Thus the record 0, 1K, and CRC, make it a "pretty slick new
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protocol" which is not significantly different from my own.
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Also, there is a catchy name - YMODEM. That means to some that it is the
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"next thing after XMODEM", and to others that it is the Y(am)MODEM
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__________
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4. VAX/VMS versions of these programs are also available.
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5. The file length, time, and file mode are optional. The pathname and
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file length may be sent alone if desired.
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Chapter 3
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X/YMODEM Protocol Reference 10-27-87 8
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protocol. I don't want to emphasize that too much - out of fear that
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other mfgrs might think it is a "competitive" protocol, rather than an
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"unaffiliated" protocol. Chuck is currently selling a much-enhanced
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version of his CP/M-80 C program YAM, calling it Professional Yam, and its
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for the PC - I'm using it right now. VERY slick! 32K capture buffer,
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script, scrolling, previously captured text search, plus built-in commands
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for just about everything - directory (sorted every which way), XMODEM,
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YMODEM, KERMIT, and ASCII file upload/download, etc. You can program it
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to "behave" with most any system - for example when trying a number for
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CIS it detects the "busy" string back from the modem and substitutes a
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diff phone # into the dialing string and branches back to try it.
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