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Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!houxm!ihnp4!alberta!khasin
From: khasin@alberta.UUCP (Khasin Teow)
Newsgroups: net.micro
Subject: Re: xmodem protocol
Message-ID: <226@alberta.UUCP>
Date: Sun, 11-Nov-84 21:00:01 EST
Article-I.D.: alberta.226
Posted: Sun Nov 11 21:00:01 1984
Date-Received: Sun, 18-Nov-84 05:24:12 EST
References: <16670@arizona.UUCP>
Organization: U. of Alberta, Edmonton, AB
Lines: 38


 ....
> 		Kelvin Nilsen at U of Arizona

i normally would reply directly to the person who posted the news.
however most of my replies seem to come back to me.  so if some of
you would bear with me:
 ...
i have been using the following algorithm:

XMODEM protocol

The description here in pseudo-code is derived from Appendix B of
Freeware's PC-TALK III User's Guide

XMODEM (receiver)
BEGIN 
	Send NAK every 10 sec.
	Read a character
	WHILE (character is SOH)
		Receive the package
		  (character 1 is block number,
		   character 2 is 1's compliment of char 1,
		   next 128 characters are data,
		   last character is check sum.)
		IF the package is ok
			Send an ACK
		ELSE
			Send a NAK
		Read a character
	ENDWHILE
	IF (character is EOT)
		Send an ACK
	ELSE
		??? (ignore it)
END of XMODEM

i hope you find it a useful pointer.