| Author |
Message |
Perdition
Guest
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 Posted:
Sun Oct 30, 2005 5:20 pm Post subject:
DTR-RI control signal simulation |
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Can someone explain the concept behind this and where it is needed
please because I only managed to find info on RTS-DCD simulation :\ |
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Reed
Guest
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| Posted:
Sun Oct 30, 2005 11:51 pm Post subject:
Re: DTR-RI control signal simulation |
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Perdition wrote:
| Quote: |
Can someone explain the concept behind this and where it is needed
please because I only managed to find info on RTS-DCD simulation :\
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Not sure where a "simulation" of DTR or RI would be needed except
possibly in a device bench test environment, or a direct DTE to
DTE crossover connection where the DTEs required a RI assertion
before it would assert DTR.
By simulation, do you mean simulating DCE/DTE signals in the
absence of real modems (aka crossover connection); or the concept
of passing the status of control signals end-to-end across a real
modem-modem connection (or a channel within a TDM)??
--reed |
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Perdition
Guest
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| Posted:
Mon Oct 31, 2005 1:40 am Post subject:
Re: DTR-RI control signal simulation |
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The latter, control signal simulation for RI-DTR, supposedly used in
old modems. |
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Reed
Guest
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| Posted:
Mon Oct 31, 2005 2:13 am Post subject:
Re: DTR-RI control signal simulation |
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Perdition wrote:
| Quote: |
The latter, control signal simulation for RI-DTR, supposedly used in
old modems.
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The application of RTS at one end controlling DCD at the other, in
my experience, was widely used in appropriate environments.
RI controlling DTR at the other end, was not. Probably intended to
implement a remote dial-in application, where the Host DTE
required an RI signal to allow a connection to be made.
As you may know, the normal sequence in the original RS-232 based
interface was:
1. Answering modem, in auto-answer mode, detects ringing on dial
line, toggles RI toward host DTE.
2. Host DTE asserts DTR, telling modem "it's OK to go off-hook",
and send answer tone.
3. Originating modem "goes to data mode", completing
modem-to-modem connection.
--reed |
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Perdition
Guest
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| Posted:
Mon Oct 31, 2005 5:20 pm Post subject:
Re: DTR-RI control signal simulation |
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awesome, thanks again reed :) by the by I was wondering about
something, in the following site http://ckp.made-it.com/sync.html the
final bit shows a modem with INT, and another with EXT, and yet it
states there is only one clock. Wouldn't it be only one clock if the
modem with EXT was a third RCV so it would be DTE -> INT -> RCV -> RCV
-> RCV -> DTE? |
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Reed
Guest
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| Posted:
Tue Nov 01, 2005 8:32 am Post subject:
Re: DTR-RI control signal simulation |
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Perdition wrote:
| Quote: | awesome, thanks again reed :) by the by I was wondering about
something, in the following site http://ckp.made-it.com/sync.html the
final bit shows a modem with INT, and another with EXT, and yet it
states there is only one clock. Wouldn't it be only one clock if the
modem with EXT was a third RCV so it would be DTE -> INT -> RCV -> RCV
-> RCV -> DTE?
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Actually, since they state that the last diagram is *without* tail circuit
buffers, both middle modems should be EXT (each pin 17 output clock wired
to others pin 24 ext clock input). Then the far left modem is source for
entire application.
You can't have the 2 modems at each end of their phone line in RCV,
otherwise they try to "chase" each other since neither is "master" source.
I also don't like the next to last diagram. In this 4 modem application,
only one can be INT, even with buffers.Their comments re
"received/recovered clock from data" are misleading, as all sync modems
recover timing from carrier & data on their receive sides. You only can
select/configure what the modem will use as a source on it's transmitting
side, be it INT, EXT (or DA timing), or RCV (or DD timing).
Their sentence in the first paragraph that reads "And when external
clocking is used the phase of the Tx clock is phase locked to the one that
is provided through the Rx clock" should say "And when external clocking
is used the phase of the Tx clock is phase locked to the external signal
input on pin 24 of the modem's interface, from some external source".
The writer is correct that this was very often a difficult concept to
explain. It was usually best to do it on a chalk/greaseboard so you could
map out the flow of the timing relationships.
--reed |
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Perdition
Guest
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| Posted:
Tue Nov 01, 2005 9:20 am Post subject:
Re: DTR-RI control signal simulation |
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well if EXT doesn't supply a clock,since INT in the last one would be
the only clock source if you have INT->EXT->EXT->RCV, then how is it
different from RCV? It's quite annoying trying to understand this from
literature :\ I read that EXT is when the modem gets its clock from the
DTE, if so then does the DTE have to be set to EXT somehow as well, I
didn't see any such option in Hyperterminal for windows. Besides if it
gets the clock from DTE then what would it mean for modems that aren't
adjacent to the DTE which are also set to EXT? |
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Reed
Guest
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| Posted:
Wed Nov 02, 2005 7:59 am Post subject:
Re: DTR-RI control signal simulation |
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Perdition wrote:
| Quote: |
well if EXT doesn't supply a clock,since INT in the last one would be
the only clock source if you have INT->EXT->EXT->RCV, then how is it
different from RCV?
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The 2 middle modems are clocking each other, but in opposite
directions via a crossover wired cable (pins 17 to 24 & 24 to 17)
| Quote: | It's quite annoying trying to understand this from
literature :\
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Agreed.
| Quote: | I read that EXT is when the modem gets its clock from the
DTE,
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Or any external source, such as another modem as above. Also some
applications (usually military) used a "station" clock derived
from some on-site "atomic" clock device that timed everything in
the communication center.
| Quote: | if so then does the DTE have to be set to EXT somehow as well, I
didn't see any such option in Hyperterminal for windows.
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HT on a PC is Async, no clocks involved. By convention,
Synchronous DTEs accept both Tx and Rx clock (pins 15 &17) from
the DCE. Modems set for INT or RCV provide both. Obviously there
are exceptions, mostly when the DTE is a Time Division Mux (TDM)
that wants to be the timing source for the application.
| Quote: | Besides if it
gets the clock from DTE then what would it mean for modems that aren't
adjacent to the DTE which are also set to EXT?
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As above , they clock each other in each direction.
--reed |
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