RS232 RTS/CTS Timing

[Sebastian Meuren]

Hi!

Sorry for this basi question, but does anybody know where I can find a
timing chart for the RS232 Hardware-Handshaking (RTS /CTS)? Everything I
find is either the information "...I don't use hardware handshaking..." or
s.th. like ".. Hardware-Handshaking over RTS/CTS is posible.." but I haven't
found any timing information yet (-;


pleas help me, thx in advance, till then, Sebastian....

 

[CFoley1064]

Subject: RS232 RTS/CTS Timing
From: "Sebastian Meuren" SebastianNeruem@GMX.de
Date: 3/19/2004 1:51 AM Central Standard Time
Message-id: <c3e8ql$26rb38$1@ID-185809.news.uni-berlin.de

Hi!

Sorry for this basi question, but does anybody know where I can find a
timing chart for the RS232 Hardware-Handshaking (RTS /CTS)? Everything I
find is either the information "...I don't use hardware handshaking..." or
s.th. like ".. Hardware-Handshaking over RTS/CTS is posible.." but I haven't
found any timing information yet (-;


pleas help me, thx in advance, till then, Sebastian....

RS-232 is asynchronous -- there's no timing diagram required for RTS/CTS on
RS-232. The sending device asserts Request To Send, and then waits. The
receiving device, at its whim and convenience, asserts Clear To Send to say
it's ready to receive. The sending device sends. Repeat as needed.

Let's assume you want to get a PC talking to a Basic Stamp. The Stamp has a
zero byte buffer -- it listens on an input pin without benefit of UART. It has
to stop what it's doing and pay attention to RxD, or either it will lose the
byte, or it won't be able to do anything else except wait for serial comm. By
using another pin as CTS, you can keep the PC from overrunning the Stamp and
causing the Stamp to miss bytes.

You can get all kinds of things talking to each other this way, but both sets
of software have to be in agreement about when to talk and when to listen.

Good luck
Chris

 

[R. Steve Walz]

Sebastian Meuren wrote:

Hi!

Sorry for this basi question, but does anybody know where I can find a
timing chart for the RS232 Hardware-Handshaking (RTS /CTS)? Everything I
find is either the information "...I don't use hardware handshaking..." or
s.th. like ".. Hardware-Handshaking over RTS/CTS is posible.." but I haven't
found any timing information yet (-;

pleas help me, thx in advance, till then, Sebastian....
----------------------------

Such detail isn't needed to use serial communications. But for info,
check:

http://www.beyondlogic.org

Or if you are probing the limits, do so experimentally in your S/W.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[petrus bitbyter]

"Sebastian Meuren" <SebastianNeruem@GMX.de> schreef in bericht
news:c3e8ql$26rb38$1@ID-185809.news.uni-berlin.de...

Hi!

Sorry for this basi question, but does anybody know where I can find a
timing chart for the RS232 Hardware-Handshaking (RTS /CTS)? Everything I
find is either the information "...I don't use hardware handshaking..." or
s.th. like ".. Hardware-Handshaking over RTS/CTS is posible.." but I
haven't
found any timing information yet (-;


pleas help me, thx in advance, till then, Sebastian....

Sebastian,

The RTS/CTS signals are part of the DTE/DCE protocol as specified in V24 of
CCITT or RS232 of EIA. In that, a DTE and a DCE are a PC and a modem
respectively for instance. In the protocol the PC asks the modem to prepare
for sending a message by activating RTS (Request To Send.) If there are no
objections (a unexpected break for instance) the modem blocks its receiver,
starts to transmit its carrier, waits for a defined time until the carrier
has stabilised and then activates CTS to report it is ready for sending.
Knowing this you will realise that other uses of this signals are not
normalised so it depends on the particular software how they are
interpreted. Most of the time they are ignored or connected together on both
sides to satisfy the UARTS. For hardware handshaking a similar set of
signals - DSR/DTR - is often used. These signals are also used in the
protocol mentioned but in an earlier stage building up a modem connection.
While improper used as handshaking signals the DTR signals are connected to
theit DSR counterparts on the other side. DTR is activated to confirm the
equipment is ready accept data. De-activating means is not ready anymore so
the transmitter has to stop sending data to prevent overrun on the other
side.

petrus


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[Dbowey]

Sebastian posted:

Sorry for this basi question, but does anybody know where I can find a
timing chart for the RS232 Hardware-Handshaking (RTS /CTS)? Everything I
find is either the information "...I don't use hardware handshaking..."
or
s.th. like ".. Hardware-Handshaking over RTS/CTS is posible.." but I haven't
found any timing information yet
-------

I checked the RS232-D, RS232-E, and an old Blue Book, and I don't find a timing
table anywhere.

The only time I found the RTS-CTS timing to be critical was in DCE used for
synchronous digital data. Because the telcos were having problems with some
customer's service, from too much time between RTS and CTS, a note about the
timing was placed in the ANSI T1 digital data Standard that was being written.
As I recall, we asked vendors to be sure to provide an option for 15 mS.
Common options were for 15 and 50 as I recall, but there were variances between
vendors. Digital data in this context means DCE designed to use a digital
channel connection to the telco. Some RTS-DTS delay was required for the DCE
changeover from sending "idle code" to sending customer data.

When the DCE was an analog modem, it was common to have receipt of RTS from the
DTE, send CTS back to the DTE with no intended delay, since there was nothing
in the DCE to "changeover."

Don

 

[petrus bitbyter]

"Dbowey" <dbowey@aol.com> schreef in bericht
news:20040320160937.21022.00000058@mb-m27.aol.com...

Sebastian posted:
Sorry for this basi question, but does anybody know where I can find a
timing chart for the RS232 Hardware-Handshaking (RTS /CTS)? Everything I
find is either the information "...I don't use hardware handshaking..."
or
s.th. like ".. Hardware-Handshaking over RTS/CTS is posible.." but I
haven't
found any timing information yet
-------
I checked the RS232-D, RS232-E, and an old Blue Book, and I don't find a
timing
table anywhere.

The only time I found the RTS-CTS timing to be critical was in DCE used
for
synchronous digital data. Because the telcos were having problems with
some
customer's service, from too much time between RTS and CTS, a note about
the
timing was placed in the ANSI T1 digital data Standard that was being
written.
As I recall, we asked vendors to be sure to provide an option for 15 mS.
Common options were for 15 and 50 as I recall, but there were variances
between
vendors. Digital data in this context means DCE designed to use a digital
channel connection to the telco. Some RTS-DTS delay was required for the
DCE
changeover from sending "idle code" to sending customer data.

When the DCE was an analog modem, it was common to have receipt of RTS
from the
DTE, send CTS back to the DTE with no intended delay, since there was
nothing
in the DCE to "changeover."

Don

Don,

It's a long, long time but we ever had problems with a software
implementation of the protocol that required a certain delay between the
activating RTS and CTS. The half-duplex (analog) modems of that age not only
used RTS/CTS when the connection was build up for the first time but also
for any changeover. Later, when we had to fake a modem we build in
presettable delays. 10 to 50ms in five steps if I remember well.

petrus


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[Watson A.Name \"Watt Sun]

Sebastian Meuren wrote:

Hi!

Sorry for this basi question, but does anybody know where I can find
a timing chart for the RS232 Hardware-Handshaking (RTS /CTS)?
Everything I find is either the information "...I don't use hardware
handshaking..." or s.th. like ".. Hardware-Handshaking over RTS/CTS
is posible.." but I haven't found any timing information yet (-;

pleas help me, thx in advance, till then, Sebastian....

Look for your information in UART specifications, and post your
questions to the appropriate newsgroup, comp.dcom.modems.