Path: utzoo!attcan!uunet!ncrlnk!ncrcae!ece-csc!ncsuvx!gatech!uflorida!mailrus!cornell!rochester!srs!dan
From: dan@srs.UUCP (Dan Kegel)
Newsgroups: comp.protocols.misc
Subject: xmodem protocol spec
Message-ID: <980@srs.UUCP>
Date: 29 Sep 88 14:09:53 GMT
Reply-To: srs!dan@cs.rochester.edu (Dan Kegel)
Organization: S.R.Systems
Lines: 88


It's been a while since I've seen the definition of the various
xmodem protocols posted.  Here is the first page of a lengthy
spec posted to net.sources in 1986; if enough people (say, 10)
ask me to post the whole thing, I will.  On the other hand,
if anybody has a more up to date version, please let me know.


Subject: Windowing XMODEM (WXMODEM) protocol proposal

--cut here--WXMODEM.DOC--cut here--
.OP
		      Xmodem, CRC Xmodem, Wxmodem
			File Transfer Protocols

	  Please circulate this document anyway that you see
	  fit without alteration except on the page at the
	  end titled: "Notes and Comments".  It is requested
	  that anyone using these protocols within a commer-
	  cial product not charge for them as an option or
	  surcharge, but include XMODEM and its derivations
	  as part of the basic product.

					Peter Boswell
					June 20, 1986
					People/Link email: TOPPER
.PA
	  Xmodem, CRC Xmodem, WXmodem
June 20, 1986						      Page 2
----------------------------------------------------------------------

			   TABLE OF CONTENTS


1.   PREFACE  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3

2.   INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . .   5

3.   TERMINOLOGY  . . . . . . . . . . . . . . . . . . . . . . . . .   6

4.   XMODEM . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1. Xmodem Hardware Level Protocol  . . . . . . . . . . . . .   7
     4.2. Xmodem Initiation . . . . . . . . . . . . . . . . . . . .   7
     4.3. Xmodem Data Transmission  . . . . . . . . . . . . . . . .   8
     4.4. Xmodem Cancellation . . . . . . . . . . . . . . . . . . .   9
     4.5. Xmodem Error Recovery and Timing  . . . . . . . . . . . .   9

5.   CRC XMODEM . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1. CRC Calculation Rules . . . . . . . . . . . . . . . . . .  13
     5.2. CRC Xmodem Initiation . . . . . . . . . . . . . . . . . .  14

6.   WINDOWED XMODEM (WXMODEM)	. . . . . . . . . . . . . . . . . .  15
     6.2. Transparency and Flow Control Rules (Byte Level Rules)  .  16
     6.3. Initial Handshake Rules . . . . . . . . . . . . . . . . .  18
     6.4. Window Packet Transmission Rules  . . . . . . . . . . . .  18
     6.5. Notes for X.25 Hosts	. . . . . . . . . . . . . . . . . .  22

7.   APPENDIX A - CRC CALCULATION RULES . . . . . . . . . . . . . .  23
     7.1. IBM PC - 8088/8086 Data Structure . . . . . . . . . . . .  23
     7.2. BASIC Implementation of Bit Shift Method  . . . . . . . .  23
     7.3. BASIC Implementation of the Table Method  . . . . . . . .  26

8.   NOTES AND COMMENTS . . . . . . . . . . . . . . . . . . . . . .  28
.PA
	  Xmodem, CRC Xmodem, WXmodem
June 20, 1986						      Page 3
----------------------------------------------------------------------

1.   PREFACE

In the years that have past since Xmodem was first developed as a file
transfer protocol, many thousands of people have been involved in
finding reasonable ways to move data via asynchronous telephone commun-
ications.  I appreciate the opportunity that I have had to meet and
learn from many of these people.  There is nothing in this document
that did not actually come from someone else.  Indeed, whether it is
WXMODEM, X.PC, Synchronous dial-up X.25, SNA, ZMODEM, Blast, Kermit or
any other protocol that becomes the dominant dial-up file transfer
protocol for personal and home computers is just not important.  What
is important is that the public domain have a high speed file transfer
protocol that is reasonably popular and  commonly available for many
types of personal computers, for bulletin boards and for services such
as People/Link, Delphi, CompuServe, GEnie and The Source.

.......
-- 
  Dan Kegel   "I am firmly anti-Semitic..."- George Bush
  srs!dan@cs.rochester.edu  rochester!srs!dan dan%srs.uucp@harvard.harvard.edu