I also found this gem, which I will put in
ftp://ftp-eng.cisco.com/billw/ymodem.doc

2-Jun-85 22:14:08-PDT,44767;000000000001
From: Chuck Forsberg WA7KGX <caf%omen.uucp@BRL.ARPA>
Newsgroups: net.micro,net.micro.pc
Subject: YMODEM (=XMODEM+1) Doc
Date: 1 Jun 85 19:30:58 GMT
To:       info-micro@brl-vgr.ARPA

*** NAK THIS LINE ***
By popular request, I am posting this document describing the XMODEM
protocol, plus the XMODEM/CRC and YMODEM (Batch transmission, etc.)
protocol extensions.

Ward Christensen's article on this subject will appear late this year
in Byte Magazine.
-------------



                                  - 1 -



                     XMODEM/YMODEM PROTOCOL REFERENCE
                 A compendium of documents describing the
                            XMODEM and YMODEM
                         File Transfer Protocols

                         Edited by Chuck Forsberg

                 Please distribute as widely as possible.

                    UUCP: ...!tektronix!reed!omen!caf


                                 CONTENTS


1.  ROSETTA STONE.....................................................   2

2.  TOWER OF BABEL ??.................................................   3
    2.1  Some Messages from the Pioneer...............................   3

3.  XMODEM PROTOCOL ENHANCEMENTS......................................   6
    3.1  CAN-CAN Abort................................................   6
    3.2  CRC-16 Option................................................   6
    3.3  1024 Byte Packet Option......................................   7

4.  YMODEM Batch File Transmission....................................   8

6.  XMODEM PROTOCOL OVERVIEW..........................................  13
    6.1  Definitions..................................................  13
    6.2  Transmission Medium Level Protocol...........................  13
    6.3  File Level Protocol..........................................  14
    6.4  Programming Tips.............................................  15

7.  XMODEM/CRC Overview...............................................  17
    7.1  CRC Calculation..............................................  17
    7.2  CRC File Level Protocol Changes..............................  18
    7.3  Data Flow Examples with CRC Option...........................  19

8.  MORE INFORMATION..................................................  21

9.  YMODEM Programs...................................................  22