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'[OT] X-modem protocol'
1998\06\15@213152 by Matt Bonner

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I've been searching, but can't find much on this.

Does anyone have a description (flow-chart, algorithm, etc) of the
Xmodem protocol?  I prefer the Xmodem-1K version (sometimes called
Ymodem) since it supports CRC instead of checksum error detection.

--Matt

1998\06\16@002318 by John Tibbits

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X-Modem:

Offset            Contents
0                    SOH = Ascii 01
1                    Block #, start with 1, wrap to 0 after FF
2                    Ones complement of block #
3-130            128 bytes of data
131                 Checksum of bytes  (carry ignored)

Best regards-
John
-----Original Message-----
From: Matt Bonner <spam_OUTmbonnerTakeThisOuTspamSUNADA.COM>
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU <PICLISTspamKILLspamMITVMA.MIT.EDU>
Date: Monday, June 15, 1998 6:34 PM
Subject: [OT] X-modem protocol


>I've been searching, but can't find much on this.
>
>Does anyone have a description (flow-chart, algorithm, etc) of the
>Xmodem protocol?  I prefer the Xmodem-1K version (sometimes called
>Ymodem) since it supports CRC instead of checksum error detection.
>
>--Matt
>

1998\06\16@073126 by hatfield

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Matt Bonner wrote:
>
> I've been searching, but can't find much on this.
>
> Does anyone have a description (flow-chart, algorithm, etc) of the
> Xmodem protocol?  I prefer the Xmodem-1K version (sometimes called
> Ymodem) since it supports CRC instead of checksum error detection.
>

I haven't fooled with XMODEM for years, but I know it is widely
used in many of the FIDONET BBS's.  You might get some information
from one of their sites.

I believe ZMODEM has all those features, plus being able to
restart from interruption point on reconnection as well.  It
has sort of become the current 'standard' among many of the
downloaders.

Fred.
.....fred.hatfieldKILLspamspam.....sstar.com

1998\06\16@111141 by WF AUTOMACAO

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Matt Bonner wrote:
>
> I've been searching, but can't find much on this.
>
> Does anyone have a description (flow-chart, algorithm, etc) of the
> Xmodem protocol?  I prefer the Xmodem-1K version (sometimes called
> Ymodem) since it supports CRC instead of checksum error detection.
>
> --Matt

Well Well, you can find at http://www.simtel.com, shareware-->DOS---> "modem"

Yesterday i was looking for more about HAYES and found about XMODEM!

Miguel.

1998\06\16@113039 by Chris Savage

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There's a reasonable description with FSM diagrams in C++
Communiccations Utilities, Holmes & Flanders, Ziff Davis Press, ISBN
1-56276-110-2. Also has a disc with C++ and 8086 asm.

If you can't find a copy I could scan the relevant pages but don't tell
Ziff I said that.

Matt Bonner wrote:
>
> I've been searching, but can't find much on this.
>
> Does anyone have a description (flow-chart, algorithm, etc) of the
> Xmodem protocol?  I prefer the Xmodem-1K version (sometimes called
> Ymodem) since it supports CRC instead of checksum error detection.
>
> --Matt

--
----------------------------------------
Chris Savage, CTIV Ltd, Egham UK
EraseMEchrisspam_OUTspamTakeThisOuTcti-vision.demon.co.uk
http://www.cti-vision.demon.co.uk

1998\06\16@145245 by William Chops Westfield

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Xmodem - the beginning.  128 byte packets as documented previously.
Ymodem - add CRC and filename negotiation.  Permits downloading of
        multiple files with a single command.  I don't think that
        ymodem added 1k packets, although that variant might exist.
Zmodem - added large packets and a sliding window for full bandwidth
        throughput.

These should all be out there and pretty well documented.  I can dig
up IBM BasicA code to do Xmodem if anyone is interested...

BillW

1998\06\16@213818 by Martin Green

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    I used to have the docs on this from my CP/M days, but they are long
    gone now. I did want to comment on a couple of points though.

    YModem is not the same as XModem-1K, although they are similar, with
    both protocols using 1K blocks. Trying to use the YModem protocol in a
    comm program to receive a file sent in XModem-1K, or vice-versa, will
    not work. There is also a version of YModem calld YModem-G that is
    intended for error-correcting modems. YModem-G has less error checking
    built in since this reduces throughput, and is redundant if the modem
    is handling error checking too.

    XModem comes in at least three flavours, the original XModem with 256
    byte blocks and checksum error handling, XModem-CRC with 256 byte
    blocks and CRC error handling, and XModem-1K, with a 1K block size and
    CRC error handling. There may be an XModem-1K that uses checksums, but
    I've never seen it. The only difference between XModem-CRC and
    XModem-1K is the block size, the number of characters sent before an
    acknowledgement is expected from the receiver. The bigger the block
    size, the lower the ratio of 'protocol traffic' to actual data, and so
    the higher the throughput of meaningful data. The downside is that if
    the block size is made bigger, then more data must be re-transmitted
    in a noisy environment if a block CRC or checksum doesn't match.


    CIAO - Martin.


______________________________ Reply Separator _________________________________
Subject: [OT] X-modem protocol
Author:  pic microcontroller discussion list <PICLISTspamspam_OUTMITVMA.MIT.EDU> at
Internet
Date:    6/15/98 3:58 PM


I've been searching, but can't find much on this.

Does anyone have a description (flow-chart, algorithm, etc) of the
Xmodem protocol?  I prefer the Xmodem-1K version (sometimes called
Ymodem) since it supports CRC instead of checksum error detection.

--Matt

1998\06\19@093914 by Nowhere Man

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Remember also that the 'window size' is 1. An ACK must be sent to the
sender before the next packet will be sent. If the checksum doesnt
match, a NAK must be sent. After 10 NAKs, the transfer should abort.
Take a look through:
http://oak.oakland.edu/pub/misc/protocols/
Specifically the protocol.doc and ymodem8.doc files. They provide a
mode verbose description of the protocols.

Paul

On Mon, 15 Jun 1998 23:05:03 -0700, you wrote:

{Quote hidden}

>{Original Message removed}

1998\06\19@102944 by Matt Bonner

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Nowhere Man wrote:

> Take a look through:
> http://oak.oakland.edu/pub/misc/protocols/

Thanks!  This is what I was looking for.

--Matt

1998\06\19@194203 by Jack Trudeau

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>Date:         Tue, 16 Jun 1998 05:52:20 GMT
>Reply-To:     pic microcontroller discussion list
<@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
{Quote hidden}

>>{Original Message removed}

1998\06\20@035102 by White Horse Design

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At 16:29 19/06/98 PDT, you wrote:
>>Date:         Tue, 16 Jun 1998 05:52:20 GMT
>>Reply-To:     pic microcontroller discussion list
><spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
>>From:         Nowhere Man <TakeThisOuTnowheremanEraseMEspamspam_OUTNOWHERE.NET>
>>Subject:      Re: [OT] X-modem protocol
>>To:           RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU
>>
>>Remember also that the 'window size' is 1. An ACK must be sent to the
>>sender before the next packet will be sent. If the checksum doesnt
>>match, a NAK must be sent. After 10 NAKs, the transfer should abort.

In the old days (before error correcting modems) it was most advantageous
to use xmodem or similar protocols for trans-atlantic BBS calls, especially
when connected via satellite. Due to the delays (with other protocols) each
end could NAK the other and both timeout! At least with xmodem each packet
was acknowledged.

With an error prone link a windowed protocol could (say) send 10 packets
then slide the window back 9 and send 9 then slide it back and.. you get
the picture. The transfer time was actually longer than using Xmodem as
result.

Regards

Adrian

WWW    WWW   Adrian Gothard
WWW WW WWW   White Horse Design
WWWWWWWWWW   +44-385-970009 (Mobile/SMS), +44-118-962-8913/4 (voice/fax)
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Developers of GPS satellite-based tracking systems for vehicles/helicopters

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