155 lines
6.9 KiB
Plaintext
155 lines
6.9 KiB
Plaintext
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Zmodem comes to GBBS!
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This past summer, between writing different versions of Shrinkit and GS-ShrinkIt, I wrote Zmodem drivers for several different bulletin board
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systems. If you are the sysop of a bulletin board which uses GBBS's ACOS
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language you can take advantage of a very good deal.
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For $21, I will send you a copy of the Zmodem drivers which work with GBBS.
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But before I go into a little more detail about this, let me explain a little
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more about the Zmodem drivers.
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Features:
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--------
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o Both RZ and SZ completely conform to the public domain Zmodem 2.0
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implementation by Chuck Forsberg using 16-bit CRCs.
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Both Zmodem Send (SZ) and Zmodem Receive (RZ) are completely and correctly
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implemented and take approximately 4k of space in the GBBS "use" buffer
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along with an extra 8k of buffer space in auxiliary memory.
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o There are special versions of RZ and SZ which use the Apple IIc's
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vertical-blanking interrupts for timing considerations.
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o Speed. Zmodem is a streaming protocol. This allows for faster transfers
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than Ymodem and helps 9600 baud transfers go close to their theoretical
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maximum.
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o Better error recovery. Zmodem can recover from errors better than Xmodem
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or Ymodem. If you have a really noisy line, chances are that Zmodem will
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continue the transfer long after Xmodem and Ymodem have given up.
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o Network friendly. RZ and SZ will not "jam" a network by sending XOFF
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characters in its data stream. Instead these characters are sent using
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Zmodem's escaping mechanism. What this means is that you won't have to
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setup your local node of PcPursuit or other service when calling a BBS
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that uses RZ and SZ. No special parameters for your node should be needed.
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Just call and transfer.
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o Zmodem is a "batch" protocol. Both drivers support sending and receiving
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batches of files.
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o Auto-Download support. If your terminal program supports Auto-Download,
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then using RZ with your BBS will automatically tell your communications
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software to begin downloading without ever touching a key!
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o Download resumption. If you have a communications program which supports
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resuming a download after you have been disconnected while downloading
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a huge file... no problem. Just call back and begin the download at the
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point where you left off. These Zmodem drivers properly support doing just
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that.
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o SZ (the BBS end receiving a file via Zmodem) supports both upload
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resumption (if you, as a sysop, like incomplete pieces of files laying
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around on your BBS), renaming an existing file, or just deleting a file
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on the BBS which the user is trying to upload. So, in the case of a
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duplicate file, you have great flexibility in what to do.
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o Automatic block resizing! Xmodem sends files with 128 byte blocks. Ymodem
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sends files with both 128 byte and 1k blocks. Zmodem can use any block
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size up to 1k. When downloading, RZ will take note of how noisy the phone
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line is and if there are enough errors RZ will halve the block size until
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some data gets through.
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If you have clean phone lines then RZ will start increasing the block size
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until it is streaming 1k blocks. So, the cleaner your phone lines are: the
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faster your transfers will be.
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If during the course of a download the phone lines become very noisy then
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RZ will make the blocks smaller -- and if the line becomes less noisy later
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during the download, RZ will start sending larger blocks.
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* Just a note. At this time, although plenty of Macintosh and IBM PC
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communications programs like ZTerm and ZComm support Auto-Download and
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file resumption, I do not know of any Apple II communications software which
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does. ProTerm 2.2 and prior do not support Auto-Download or file
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resumption, although it is conceivable that ProTerm 3.0 will (we can hope).
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What you need to use RZ and SZ:
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------------------------------
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An enhanced (65c02) 128k Apple IIe, IIc, or Apple IIGS
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GBBS "Pro" 1.3 or later (preferably later)
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A good working knowledge of GBBS's language, ACOS.
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What your $21 will get you:
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--------------------------
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SZ and SZC (Send Zmodem and Send Zmodem for the Apple IIc)
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RZ and RZC (Receive Zmodem and Receive Zmodem for the Apple IIc)
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Notes on how to write a simple module for your BBS to support Zmodem
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transfers.
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The latest versions of ShrinkIt, GS-ShrinkIt, II+ ShrinkIt, and
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AUTO-Unshrinkit will be included as a bonus (since they are, after all,
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freely available).
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Because I am keenly aware of the amount of piracy that a product like this
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will undergo, the following stipulations have to be attached:
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o Please pay by check. Orders received in cash will be returned.
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o I will wait up to 3 months until I have received 40 orders before shipping
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anyone's order. This means that the sooner I receive 40 orders, the sooner
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everyone will receive their copy of Zmodem for GBBS. If you are not
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prepared to wait a while -- because I can't predict how long it will take
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to receive 40 orders -- then please do not order this.
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o If I do not receive 40 orders, I will return everyone's checks uncashed.
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o I am not going to attempt to hunt down those who choose to illegally
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distribute what I write -- I would only hope that some of them have the
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decency to pay for what they use. There isn't any tomfoolery in the
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drivers either. No secret codes or encryption or serial numbers. If you
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buy a copy, I will send you a copy. It's as simple as that.
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If this sounds reasonable to you, then send a check for $21 to:
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Andy Nicholas
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1180 Reed Ave, Apt 12
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Sunnyvale, CA 94086
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and make sure you specify what kind of disk (3.5" or 5.25") on which you need
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the Zmodem drivers -and- where to send the Zmodem drivers.
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About the Author:
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----------------
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I've written the freeware programs ShrinkIt, GS-ShrinkIt, ShrinkIt for the
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Apple II+, and AUTO-UnShrinkIt (shrinkit archive scavenger/extractor) and am
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currently employed by Apple Computer to work on the Apple IIGS Finder. This
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is work that I did before coming to Apple and work that I'm doing in my spare
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time. I believe in low-cost, high-quality software. I also believe in trying
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to get that software to as many people as possible.
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At this time (1/27/91), there are tentative plans for the distribution of
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Zmodem drivers for both ProLine and the Prime BBS system. These Zmodem
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drivers have already been written and tested, although I will almost
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certainly not handle their distribution.
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If you have questions about the Zmodem drivers, suggestions for future
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versions of ShrinkIt, or suggestions for the Apple IIGS Finder, I can be
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contacted on America-Online, GEnie, CompuServe, and the internet at:
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America-Online & Genie: shrinkit
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CompuServe: 70771,2615
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Internet: shrinkit@apple.com
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