http://groups.google.com/d/topic/comp.dcom.modems/nDZ8ZIASqfo/discussion
`comp.dcom.modems ›
`Break definition
`17 posts by 13 authors
`John Antypas
`9/7/88
`I purchased a California Communications Corp. 2400 baud internal modem.
`Overall, it works just fine under Unix, but I have yet to be able to
`send a "break tone". The problem appears to be that CCC didn't know how
`to handle a break. They claim the modem has a litteral serial port
`on it so there should be no problems but...
`CCC is willing to correct the problem but they need to know how to handle
`the break. After all, there is no such thing as a break character. What
`must they do to send a break and what do they do when a "break" is received?
`How do external modems do this?
`Many thanks.
`Click here to Reply
`Michael H. Warfield
`9/8/88
`- hide quoted text -
`In article <402@ucrmath.UUCP> jantypas@ucrmath.UUCP (John Antypas) writes:
`>I purchased a California Communications Corp. 2400 baud internal modem.
`>Overall, it works just fine under Unix, but I have yet to be able to
`>send a "break tone". The problem appears to be that CCC didn't know how
`>to handle a break. They claim the modem has a litteral serial port
`>on it so there should be no problems but...
`CCC is willing to correct the problem but they need to know how to handle
`>the break. After all, there is no such thing as a break character. What
`>must they do to send a break and what do they do when a "break" is received?
`>How do external modems do this?
`
`>>
`
`>
`
` A break is sent on an async line by placing the line in
`the "low" or "spacing" state (level, tone, what-ever) for two or
`more charracter times. To a receiver this would be seen as a
`charracter of all zeros, with a framing error (no stop bit) and
`lasting at least 20 bit times (16 data bits plus 2 start bits
`plus two stop bits total across the 2 charracter times). Note
`that that is AT LEAST. Some UARTS support long and short breaks
`where short breaks are of the same order of magnitude as two
`charracter times but a long break may be 1/4 second or longer!
`The modem per se should have little to do with a break (he simply
`holds his transmission to send a looooonnnnnnngggggg series of
`zero bits) but the UART or SIO has everything to do with it.
`Some modems will, however, disconnect and drop carrier in the
`event of a "long break". Some, but not all.
`Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw
` (404) 270-2170 / 270-2098 | m...@wittsend.LBP.HARRIS.COM
`An optimist believes we live in the best of all possible worlds.
`A pessimist is sure of it!
`DugalJP
`9/8/88
`In article <402@ucrmath.UUCP> jantypas@ucrmath.UUCP (John Antypas) writes:
`>I purchased a California Communications Corp. 2400 baud internal modem.
`>Overall, it works just fine under Unix, but I have yet to be able to
`>send a "break tone". The problem appears to be that CCC didn't know how
`>to handle a break. They claim the modem has a litteral serial port
`>on it so there should be no problems but...
`CCC is willing to correct the problem but they need to know how to handle
`
`>>
`
`Page 1 of 8
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`

`
`>the break. After all, there is no such thing as a break character. What
`A break can be detected by many UARTS as a NULL received with a framing
`error. Think of a break as a start bit that persists for much longer that
`a character time, perhaps 250 ms. Many uarts can be programmed to send a
`break with a special order, but if not, changing to the slowest baud and
`sending a null might work. This of course is a real kludge and has nasty
`side effects if the uart can't support different send and receive bauds.
`Good luck getting your modem fixed ... I'm doubtful they'll fix it.
`You may be able to add a break switch to your modem by modifying the
`input to the RS232 line driver chip.
`--
`-- James Dugal, N5KNX USENET: ...!{dalsqnt,killer}!usl!jpd
`Associate Director Internet: j...@usl.edu
`Computing Center US Mail: PO Box 42770 Lafayette, LA 70504
`University of Southwestern LA. Tel. 318-231-6417 U.S.A.
`Rick Richardson
`9/9/88
`In article <60...@galbp.LBP.HARRIS.COM> mhw@wittsend.UUCP (Michael H. Warfield) writes:
`> A break is sent on an async line by placing the line in
`>the "low" or "spacing" state (level, tone, what-ever) for two or
`>more charracter times. To a receiver this would be seen as a
`>charracter of all zeros, with a framing error (no stop bit) and
`>lasting at least 20 bit times (16 data bits plus 2 start bits
`>plus two stop bits total across the 2 charracter times). Note
`>that that is AT LEAST. Some UARTS support long and short breaks
`Where did you find the citation that a break is at least 20 bit times?
`The only citation I could find (in some obscure CCITT spec) defined
`break as the space condition for at least 130 milliseconds. There
`was no formula based on the bps that the interface was operating at.
`I'm not saying you are wrong, just that a while back I tried to
`find this information and wasn't really happy with finding just
`the one definition. I'm also not saying that all devices do this.
`There are definitely devices that work the way you describe.
`I believe that sending break as 130 milliseconds or longer of space (0)
`is a better definition, though. No matter what the receiver
`speed is set to (if greater than 110 bps), the receiver is
`guaranteed to see a break.
`I think the best bet is to try to detect short breaks if you
`can, but always generate at least the full 130 milliseconds,
`if not longer. Then again, a modem, or other communications (DCE)
`device, should attempt to reconstruct the signal at the far end
`as near as possible to the way it came in at the near end.
`Garbage in...garbage out!!!! Short breaks in, short breaks out.
`--
` Rick Richardson, PC Research, Inc.
` rick%pcrat.uucp@uunet.uu.net (INTERNET)
` uunet!pcrat!rick (UUCP, Personal Mail)
`..!pcrat!jetroff (JetRoff Info) ..!pcrat!dry2 (Dhrystone Submissions)
`Henry Spencer
`9/10/88
`In article <60...@galbp.LBP.HARRIS.COM> mhw@wittsend.UUCP (Michael H. Warfield) writes:
`>>CCC is willing to correct the problem but they need to know how to handle
`>>the break. After all, there is no such thing as a break character. What
`>>must they do to send a break and what do they do when a "break" is received?
`>>How do external modems do this?
`>The modem per se should have little to do with a break (he simply
`>holds his transmission to send a looooonnnnnnngggggg series of
`>zero bits) but the UART or SIO has everything to do with it.
`At 300 baud, yes. At 2400, not so. Higher-speed modems are *NOT* just
`transmitting the RS232 signal as tones; they are actually receiving the
`characters, packaging them up in odd ways (e.g. more than one bit per line
`transition), and reversing the process at the other end. This means that
`
`Page 2 of 8
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`
`the RS232 signal has to make sense (that's why fast modems have settings
`for things like number of bits per character). It also means that
`break requires special attention, since it is *not* a character! Tell
`CCC to look up the V.22bis spec, which describes the signals on the wire
`for a 2400-baud modem; it will tell them how to send a break over the
`wire, and with luck will also tell them exactly when to send one and what
`to do when they receive one.
`Don't be too optimistic. If CCC does not know this stuff already, I
`wouldn't buy a modem from them if it cost $4.95. They are incompetent.
`They are not the only ones; this problem has been seen before.
`--
`NASA is into artificial | Henry Spencer at U of Toronto Zoology
`stupidity. - Jerry Pournelle | uunet!attcan!utzoo!henry he...@zoo.toronto.edu
`mhy...@cup.portal.com
`9/11/88
`In message <569@pcrat.UUCP> rick@pcrat.UUCP (Rick Richardson) asks:
`> Where did you find the citation that a break is at least 20 bit times?
`> The only citation I could find (in some obscure CCITT spec) defined
`> break as the space condition for at least 130 milliseconds. There
`> was no formula based on the bps that the interface was operating at.
`First some background:
` The bit (not baud) rate between the DTE side and the TELCO side of a
`modem may differ. Using V.22bis (standard 2400 bps modem) as an example:
`The spec calls for an TELCO bit rate of 2400 b/s +/- 0.01%. The DTE side
`is allowed the range of 2400 b/s +1.0%, -2.5%. [+2.3%, -2.5% in modems with
```extend signalling rate range (optional)'' implemented].
` To handle the possible overspeed on input a modem is allowed to delete
`stop bits now and again (no more than one stop bit deleted in every 8
`characters sent [4 characters with extended option]). When the receiving
`modem receives a character with a missing stop bit from the TELCO it adds
`a stop bit to the DTE. It makes time for the added stop bit by making it
`and the next 7 stop bits 12.5% shorter than a standard bit. [25% shorter
`for the next 4 stop bits with the extended option].
` What does this have to do with a break? A break must be ``2M + 3'' bits
`long at the receiver. This requirement allows the receiver to tell the
`difference between a break and consecutive NULL characters, the first with
`a deleted stop bit. Section 4.1.3 of V.22bis says:
` If the converter detects M to 2M + 3 bits all of ``start''
` polarity, where M is the number of bits per character in the
` selected format, the converter shall transmit 2M + 3 bits of
` ``start'' polarity.
`M is typically 10 in async mode and 8 in sync mode.
`--Marc
`Marco S. Hyman ...!sun!portal!cup.portal.com!mhyman
` mhyman@cup.portal.com
`Carl S. Gutekunst
`9/12/88
`Break definition (Some Answers from the Standards, LONG)
`>Higher-speed modems are *NOT* just transmitting the RS232 signal as tones;
`>they are actually receiving the characters, packaging them up in odd ways
`>(e.g. more than one bit per line transition), and reversing the process at
`>the other end.
`Um, this is rather oversimplified. Allow to me explain, and in doing so give a
`partial answer to the original question. There are several levels of things
`going on here, each of which impose their own constraints.
`First is the modulation scheme: how bits are encoded on the wire. All modems
`at 300 bits-per-second or slower use frequency shift keying (FSK), which just
`means that one tone means a mark (1) bit, and another tone means a space (0).
`Note that an FSK modem is _ n_ o_ t transmitting bits _ p_ e_ r_ _ s_ e; it is sending
`out
`
`Page 3 of 8
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`
`the current state of the RS-232 Transmit Data line as a tone. The line can
`change state whenever it wishes, and the modem will follow.
`Modems at 1200 bps and above all use some kind of phase-shift encoding, where
`multiple bits of data are encoded into a single phase shift of a carrier tone.
`Bell 212 and V.22 (1200 bps) use phase encoding (PE), where a pair of bits are
`represented by one of four phase changes: 0, 90, 180, or 270 degrees. V.22bis
`(2400 bps) modems use quadrature amplitude modulation (QAM), in which two bits
`specify an x-y quadrant, and two more bits specify a shift of phase and ampli-
`tude within the quadrant; so four bits are encoding in a single state change.
`In V.29 (9600 bps), the first bit specifies amplitude, and the next three
`specify phase angle (0, 45, 90, 135, etc.); again, 4 bits are encoded into a
`single state change.
`V.32 (9600bps full duplex) defines two schemes: QAM similar to V.22bis, and a
`five-bit variation of QAM called trellis coding. In trellis coding, four bits
`are still encoded into a single state change, but a "redundant" bit is also
`calculated, for 32 distinct QAM states. (Anybody know how trellis coding got
`that name? I'd guess that is comes from the way that two of the data bits and
`the redundant bit are permuted based on the bits in the previous five-bit
`group. The bits climb all over themselves, like flowers climbing a trellis.)
`In each case there exists a precise one-to-one relationship between _ b_ i_ t_ s
`on the digital side and state changes on the wire. This is very different from
`FSK, which is insensitive to bit boundaries. But note that the phase-encoding
`techniques remain insensitive to _ c_ h_ a_ r_ a_ c_ t_ e_ r framing. All characters are
`just
`concatenated strings of bits, and break is just a string of space bits.
`These high-speed standards were all designed for synchronous communications,
`in which all the bits dance in lockstep to the beat of the modem's clock. In
`asynchronous (which is what we all use for dialup and UUCP), the data bits are
`framed according to the transmitter's internal clock. This clock will almost
`certainly not even be the same speed (much less the same phase) as the modem's
`clock. This creates a major dilema: the modem _ m_ u_ s_ t run at exactly its nominal
`bits-per-second speed, but it has no control over the speed of the data being
`sent to it.
`So the V.22bis standard provides a lengthy set of rules for how asychronous
`devices must behave. The critical elements of the V.22bis asynchronous speci-
`fication are:
`- The amount by which the asynchronous bit rate may deviate from the nominal
` speed of 2400bps. If the transmitter is running a little faster, then the
` modem must occasionally discard stop bits. If the transmitter is running
` slow, then the modem has to occassionally add stop bits.
`- The precise specification of a break signal: from _ M to 2_ M+3 consecutive
` start (space) bits, where 'M' is the number of bits per character. In fact,
` if the modem receives a break shorter than 2M+3 bit times, it is required to
` extend it to the full time. Breaks longer than 2M+3 bits are passed through
` for their full duration. And a break must always be followed by 2_ M stop
` (mark) bits, to allow the receiver to resynchronize.
`So, the real reason why fast modems need to know how many bits-per-character
`are being used is so they know where the stop bits are. And breaks are defined
`so that the modems will know when the normal progression of character frames
`is disrupted. (By the way, V.22bis only allows character sizes of 8, 9, 10,
`and 11 bits. Those of us in the UNIX and PC worlds always use is 10 bits: 1
`start; 8 data; 1 stop.)
`An added restriction arises in all _ p_ r_ a_ c_ t_ i_ c_ a_ l implementations of
`V.22bis and
`other high-speed modems: they use microprocessors and UART chips. UART chips,
`being character oriented devices, are very fussy about character framing. :-)
`Finally, modern modems are often "smart." At the least, they accept command
`strings to do autodialing and set options. At the most, they have modem proto-
`cols like Microcom's MNP and Telebit's PEP that bundle up characters, strip
`off the start and stop bits, perform compression, and do a lot of other char-
`acter-oriented shredding. Here there is actual interpretation of the data
`going on, and the modem's CPU needs to know a lot more about the data than it
`does to simply satisfy the encoding scheme.
`None of which answers the original question. :-)
`The problem is that the CCC is an internal modem. When dealing with an exter-
`nal modem, you talk to a serial interface on the PC. The serial interface has
`a UART chip on it (a Signetics 8251, I recall). And the UART has a control
`
`Page 4 of 8
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`

`
`port with a bit in it that, when set by the CPU, drives the Transmit Data line
`into the space state. To send a break, the CPU sets this bit, spins for the
`appropriate number of CPU cycles, and then clears the bit. Voila, a break.
`For the CCC modem, then vendor has to supply something equivalent: a bit that
`you can assert to cause a break. If they are really clever, they'll make it a
`toggle, so that the modem itself will time the break rather that you having to
`use the PC's CPU or timer to do it. An ugly alternative is an escape sequence:
`you send a magic sequence of characters, and the modem sends a break. My Cerm-
`etek 199A modem does this, and it's useless; UUCP uses *all* the characters,
`so I have to disable the modem's escape character.
`<csg>
`Carl S. Gutekunst
`9/12/88
`Break definition (Some Answers from the Standards, LONG)
`Someone's gonna flame me for it elsewise, so I suppose I should mention how a
`Telebit TrailBlazer works. (I suppose this is preaching to the choir, but if
`you've carried through this far I might as well finish the job.)
`The TrailBlazer uses a proprietary modulation scheme called Dynamic Adaptive
`Multicarrier Quadrature Amplitude Modulation (DAMQAM). Rather than the single
`high-frequency carrier used by other modulation schemes, the TrailBlazer uses
`511 different low-frequency carriers. Each is QAM modulated at a rate of 12
`baud (that is, 12 state changes per second); so each carrier has a data rate
`of 48 bits per second. Each carrier can be slowed down to 8 or 4 baud (32 or
`16 bps), or dropped entirely. On real phone lines, quite a few carriers are
`dropped, and a number are slowed down to 8 baud; so the theoretical speed of
`24528 bits per second is reduced to a real maximum of 18031. (Why an odd num-
`ber? I don't know.) Note that since DAMQAM modulation broadcasts across the
`entire bandwidth of the telephone line, it is half duplex -- only one end can
`be transmitting at a time.
`On top of DAMQAM, Telebit uses a proprietary data packetizing scheme, the
`Packetized Ensemble Protocol (PEP) that we've all come to know and love. PEP
`incorporates error correction, and a family of dataflow prediction schemes
`that make the modem appear to be full-duplex. This latter process is called
`"Adaptive Duplex," a term to which both Telebit and Racal-Vadic claim trade-
`marks (the latter for the RV 9600-VP modem).
`PEP and DAMQAM are trademarks of Telebit Corp, too. MNP is a trademark of
`Microcom. But you knew that, didn't you?
`<csg>
`Anthony A. Datri
`9/13/88
`Break definition (Some Answers from the Standards, LONG)
`In article <39...@pyramid.pyramid.com> c...@pyramid.pyramid.com (Carl S. Gutekunst)
`writes:
`>means that one tone means a mark (1) bit, and another tone means a space (0).
`>Note that an FSK modem is _ n_ o_ t transmitting bits _ p_ e_ r_ _ s_ e; it is sending
`out
`So *that's* why modems are rated at 0-300 baud, not just 300 baud. I could
`_ n_ e_ v_ e_ r understand that before.
`--
`@disclaimer(Any concepts or opinions above are entirely mine, not those of my
` employer, my GIGI, or my 11/34)
`beak is beak is not
`Anthony A. Datri,SysAdmin,StepstoneCorporation,stpstn!aad
`Michael H. Warfield
`9/13/88
`In article <569@pcrat.UUCP> rick@pcrat.UUCP (Rick Richardson) writes:
`>In article <60...@galbp.LBP.HARRIS.COM> mhw@wittsend.UUCP (Michael H. Warfield) writes:
`>> A break is sent on an async line by placing the line in
`>>the "low" or "spacing" state (level, tone, what-ever) for two or
`>>more charracter times. To a receiver this would be seen as a
`
`Page 5 of 8
`
`

`
`>>charracter of all zeros, with a framing error (no stop bit) and
`>>lasting at least 20 bit times (16 data bits plus 2 start bits
`>>plus two stop bits total across the 2 charracter times). Note
`>>that that is AT LEAST. Some UARTS support long and short breaks
`Where did you find the citation that a break is at least 20 bit times?
`>The only citation I could find (in some obscure CCITT spec) defined
`>break as the space condition for at least 130 milliseconds. There
`>was no formula based on the bps that the interface was operating at.
`
`>>
`
`>
`
` Point taken. The information I was quoting was based on
`several USART chip specs (I know, I know, bad move) and not on
`any particular specification. At this point I have seen the
`references in the chip specs, as well as other feed-back from the
`net specifing anything from 100 msec on up (250 msec seems a
`common opinion). I would also like to see some hard fast specs
`on this as well. None of my comms references mention specific
`timings and I have little to go on outside of the specs I have on
`hand ( Yeah, I guess when it comes to manufacture's specs,
`there's a sucker born every minute ;-) ).
`- hide quoted text -
`Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw
` (404) 270-2170 / 270-2098 | m...@wittsend.LBP.HARRIS.COM
`An optimist believes we live in the best of all possible worlds.
`A pessimist is sure of it!
`Brad Templeton
`9/14/88
`Break definition (Some Answers from the Standards, LONG)
`But if DAMQAM is really a broadband scheme with 511 carriers using up
`the entire band, why do all 511 of the carriers have to be in the
`same direction? In interactive mode at least, I wish they always had
`at least one carrier in each direction, so that no turnaround would be
`required.
`In fact, even if having a reverse direction carrier meant you couldn't
`use several of the nearby bands in the forward direction, it would still
`be worth it in interactive mode. Ideally it would be nice to see 2
`permanent carriers in each direction, and 507 switchable carriers.
`(You may need more than 2 to achieve the information rate required with
`error correction, but you get the gist. 100 bps would be adequate for
`typing and ACK/NAKs of other protocols.)
`--
`Brad Templeton, Looking Glass Software Ltd. -- Waterloo, Ontario 519/884-7473
`Spencer Garrett
`9/14/88
`Trailblazer details
`In article <39...@pyramid.pyramid.com>, c...@pyramid.pyramid.com (Carl S. Gutekunst)
`writes:
`- The TrailBlazer uses a proprietary modulation scheme called Dynamic Adaptive
`- Multicarrier Quadrature Amplitude Modulation (DAMQAM). Rather than the single
`- high-frequency carrier used by other modulation schemes, the TrailBlazer uses
`- 511 different low-frequency carriers. Each is QAM modulated at a rate of 12
`- baud (that is, 12 state changes per second); so each carrier has a data rate
`- of 48 bits per second. Each carrier can be slowed down to 8 or 4 baud (32 or
`- 16 bps), or dropped entirely. On real phone lines, quite a few carriers are
`- dropped, and a number are slowed down to 8 baud; so the theoretical speed of
`- 24528 bits per second is reduced to a real maximum of 18031. (Why an odd num-
`- ber? I don't know.) Note that since DAMQAM modulation broadcasts across the
`- entire bandwidth of the telephone line, it is half duplex -- only one end can
`- be transmitting at a time.
`Not quite right. The Blazer runs at 7.58 baud (132 ms) when it has
`data to send. Rev 4.0 and later use a shorter time when they're idle.
`There are 511 discrete frequencies each of which can encode 0, 2, 4, or 6
`bits, but the baud rate doesn't change. The modem can't or won't
`use all of the channels at once (I don't know why). It seems to
`max out at 2380 bits per packet, and 18031 is just 2380 * 7.58,
`more-or-less.
`David Goodenough
`
`Page 6 of 8
`
`

`
`9/15/88
`From article <402@ucrmath.UUCP>, by jantypas@ucrmath.UUCP (John Antypas):
`- hide quoted text -
`> I purchased a California Communications Corp. 2400 baud internal modem.
`> Overall, it works just fine under Unix, but I have yet to be able to
`> send a "break tone". The problem appears to be that CCC didn't know how
`> to handle a break. They claim the modem has a litteral serial port
`> on it so there should be no problems but...
` CCC is willing to correct the problem but they need to know how to handle
`> the break. After all, there is no such thing as a break character. What
`> must they do to send a break and what do they do when a "break" is received?
`> How do external modems do this?
` Many thanks.
`I read this with a great deal of concern. I run a 1200 BPS modem, which
`is (in efferct) a bit transmitter: I throw a stream of bits into it,
`and they come out the far end. I know this to be the case, because on
`one occasion the getty here at lakart got stuck at 300 BPS, but with
`modems swapping 1200 BPS carrier. So I just dropped my terminal speed
`to 300, logged in, did a stty 1200, and re adjusted my local speed, and
`all was well.
`Reading between the lines of the above posting it would seem that 2400
`BPS modems are character transmitters, which means they are going to
`break a lot of things for me. For example I call in 7e1 to talk text
`with lakart, but if I'm going to do an Xmodem transfer, I have to set
`my end to 8n2 to get it to go. Now if the modem is hooked on the notion
`of 7e1, I'm in real trouble. How are other people getting around this,
`or is it not a real problem, and I don't have a clue what I'm talking
`about.
`--
` dg@lakart.UUCP - David Goodenough +---+
` | +-+-+
` ....... !harvard!cca!lakart!dg +-+-+ |
` +---+
`Steven Bellovin[jsw]
`9/16/88
`Break definition (Some Answers from the Standards, LONG)
`My thanks to c...@pyramid.pyramid.com (Carl S. Gutekunst) for an
`excellent article. One point I should add: many (most? all?) modems
`use a ``long break'' -- on the order of 3 seconds -- to indicate
`disconnect. That is, modems can be strapped so that when they wish to
`hang up (for example, if the host drops DTR), they will first transmit
`a 3-second break to the remote modem. Similarly, when they receive
`such a break signal, they will hang up, too. I suspect (but do not
`know for certain) that this usage dates back to half-duplex modems,
`which of necessity do not transmit a continuous carrier. Rather, they
`only generate carrier when they wish to transmit. Thus, the remote end
`cannot tell when the local end has hung up -- no carrier may simply
`mean that the modem doesn't have anything to say.
` --Steve Bellovin
`George Robbins
`9/16/88
`Break definition (Some Answers from the Standards, LONG)
`In article <10...@ulysses.homer.nj.att.com> s...@ulysses.homer.nj.att.com (Steven
`Bellovin[jsw]) writes:
`> My thanks to c...@pyramid.pyramid.com (Carl S. Gutekunst) for an
`> excellent article. One point I should add: many (most? all?) modems
`> use a ``long break'' -- on the order of 3 seconds -- to indicate
`> disconnect.
`It might be more accurate to state that most "traditional" modems have
`this as one of their AT&T modem compatible strapping options. It's
`normally called "long space disconnect" though... Most modems are
`configured to disconnect after n seconds without carrier, making the
`
`>>
`
`>>
`
`Page 7 of 8
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`

`
`option a somewhat passe.
`--
`George Robbins - now working for, uucp: {uunet|ihnp4|rutgers}!cbmvax!grr
`but no way officially representing arpa: cbmvax!g...@uunet.uu.net
`Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
`George Robbins
`9/16/88
`Break definition (Some Answers from the Standards, LONG)
`In article <2035@looking.UUCP> brad@looking.UUCP (Brad Templeton) writes:
`> But if DAMQAM is really a broadband scheme with 511 carriers using up
`> the entire band, why do all 511 of the carriers have to be in the
`> same direction? In interactive mode at least, I wish they always had
`> at least one carrier in each direction, so that no turnaround would be
`> required.
` In fact, even if having a reverse direction carrier meant you couldn't
`> use several of the nearby bands in the forward direction, it would still
`> be worth it in interactive mode. Ideally it would be nice to see 2
`> permanent carriers in each direction, and 507 switchable carriers.
`> (You may need more than 2 to achieve the information rate required with
`> error correction, but you get the gist. 100 bps would be adequate for
`> typing and ACK/NAKs of other protocols.)
`The disparity between transmitted and received signal levels mean that
`you need either fairly sophisticated processing or a wide guard band
`to prevent interference. Obviously it could be done, and might be a
`real win.
`Note that 100 bps is probably ok for typing, but some protocols, for
`example uucp "g", require a backwards channel of somewhere between
`300 and 600 bps to keep up with 9600 baud forward. Tis why the
`USR Courier HST isn't the magic modem for uucp...
`> --
`> Brad Templeton, Looking Glass Software Ltd. -- Waterloo, Ontario 519/884-7473
`--
`George Robbins - now working for, uucp: {uunet|ihnp4|rutgers}!cbmvax!grr
`but no way officially representing arpa: cbmvax!g...@uunet.uu.net
`Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
`mhy...@cup.portal.com
`9/17/88
`In article <248@lakart.UUCP> dg@lakart.UUCP (David Goodenough) asks:
`> break a lot of things for me. For example I call in 7e1 to talk text
`> with lakart, but if I'm going to do an Xmodem transfer, I have to set
`> my end to 8n2 to get it to go. Now if the modem is hooked on the notion
`> of 7e1, I'm in real trouble. How are other people getting around this, ...
`At 300 bps the modem encodes 1 bit per baud; when the signal at the RS-232
`port changes the modem sends a different frequency. That's why modems
`are rated 0-300 bps. At the higher frequencies multiple bits are encoded
`per baud. The modem needs to know the character size (but not the parity)
`so it may drop a stop bit when needed. The receiving modem needs to know
`the character size so it can tell when it has to insert a stop bit.
`Most modems these days assume a character size of 10 bits. If you look
`at a Smartmodem 2400 manual (page A25) you'll see that all supported
`Asynchronous data formats add up to 10 bit characters.
`--Marc
`Marco S. Hyman
`...!sun!portal!cup.portal.com!mhyman
`mhy...@cup.portal.com
`
`>>
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