Technical UART/RS-232 question

Hi group. I have a question about UART stuff, and it's fairly technical.

I'm wondering if I can run full-duplex communication between two
devices using _only_ TD, RD, RTS, CTS signals, due to hardware
limitations. I haven't a lot of experience with serial comms, and I
was wondering if someone in this group did.

I understand that half-duplex is a possibility using only the four
signals listed, but am confused at the differences. Are the extra
control signals needed because two communication signals can be sent
at any time?

Am I barking up the wrong forest?

thanks,
ed.

On 11 Apr 2005 00:53:05 +0950 in comp.periphs, eddie
<ed (AT) somewhere (DOT) that.doesnt.exist.com> wrote:

Hi group. I have a question about UART stuff, and it's fairly technical.

I'm wondering if I can run full-duplex communication between two
devices using _only_ TD, RD, RTS, CTS signals, due to hardware
limitations. I haven't a lot of experience with serial comms, and I
was wondering if someone in this group did.

I understand that half-duplex is a possibility using only the four
signals listed, but am confused at the differences. Are the extra
control signals needed because two communication signals can be sent
at any time?

Maybe -- depends on the hardware and software at each end.
Some hardware won't work if it doesn't see DTR/DSR.
Some software won't work if it doesn't see some of DSR/CD/RI.
Some hardware/software won't work if it doesn't see RTS/CTS.
Read the CCITT V.24/RS 232C, comm equipment, OS comm, and comm
software specs; and buy a breakout box that allows jumpering signals
and levels.

--
Thanks. Take care, Brian Inglis Calgary, Alberta, Canada

Brian.Inglis (AT) CSi (DOT) com (Brian[dot]Inglis{at}SystematicSW[dot]ab[dot]ca)
fake address use address above to reply

Brian Inglis <Brian.Inglis (AT) SystematicSW (DOT) Invalid> wrote in
news:50vi51posjmr0v28101h88gs5vnavk32mk (AT) 4ax (DOT) com:

On 11 Apr 2005 00:53:05 +0950 in comp.periphs, eddie
ed (AT) somewhere (DOT) that.doesnt.exist.com> wrote:

Hi group. I have a question about UART stuff, and it's fairly
technical.

I'm wondering if I can run full-duplex communication between two
devices using _only_ TD, RD, RTS, CTS signals, due to hardware
limitations. I haven't a lot of experience with serial comms, and I
was wondering if someone in this group did.

I understand that half-duplex is a possibility using only the four
signals listed, but am confused at the differences. Are the extra
control signals needed because two communication signals can be sent
at any time?

Maybe -- depends on the hardware and software at each end.
Some hardware won't work if it doesn't see DTR/DSR.

The hardware at one end is fixed (the four signals), and software
can be written as needed. The hardware at the other end is variable,
as is any possible software. AFAIK there aren't any DTR, DSR signals
available.

Some software won't work if it doesn't see some of DSR/CD/RI.
Some hardware/software won't work if it doesn't see RTS/CTS.
Read the CCITT V.24/RS 232C, comm equipment, OS comm, and comm
software specs; and buy a breakout box that allows jumpering signals
and levels.

Sorry to sound like a whiner, but having trouble finding 1) a copy of
the spec, 2) a way to get the spec (a few hours on google missed the
mark :|...). Strangely enough the UART is going to be operating as
a sim of hardware, so information is the problem at the moment.

The way I see it, there's a very simple way possibly...
A says "I'm ready to receive" over line 1, and B starts sending,
A says "I'm not ready to receive" over line 1, and B stops sending.
Invert A and B, communicate over line 2 and you have a primitive
full-duplex. However, if the only control lines you have are
RTS/CTS - which, from extra reading I've done, are for flow control
then I think I'm barking up the wrong tree. I'll have a look at the
sim code I think...

ed.

On 12 Apr 2005 00:09:22 +0950 in comp.periphs, eddie
<ed (AT) mysterious (DOT) dark.places.com> wrote:

Brian Inglis <Brian.Inglis (AT) SystematicSW (DOT) Invalid> wrote in
news:50vi51posjmr0v28101h88gs5vnavk32mk (AT) 4ax (DOT) com:

On 11 Apr 2005 00:53:05 +0950 in comp.periphs, eddie
ed (AT) somewhere (DOT) that.doesnt.exist.com> wrote:

Hi group. I have a question about UART stuff, and it's fairly
technical.

I'm wondering if I can run full-duplex communication between two
devices using _only_ TD, RD, RTS, CTS signals, due to hardware
limitations. I haven't a lot of experience with serial comms, and I
was wondering if someone in this group did.

I understand that half-duplex is a possibility using only the four
signals listed, but am confused at the differences. Are the extra
control signals needed because two communication signals can be sent
at any time?

Maybe -- depends on the hardware and software at each end.
Some hardware won't work if it doesn't see DTR/DSR.

The hardware at one end is fixed (the four signals), and software
can be written as needed. The hardware at the other end is variable,
as is any possible software. AFAIK there aren't any DTR, DSR signals
available.

Some software won't work if it doesn't see some of DSR/CD/RI.
Some hardware/software won't work if it doesn't see RTS/CTS.
Read the CCITT V.24/RS 232C, comm equipment, OS comm, and comm
software specs; and buy a breakout box that allows jumpering signals
and levels.

Sorry to sound like a whiner, but having trouble finding 1) a copy of
the spec, 2) a way to get the spec (a few hours on google missed the
mark :|...). Strangely enough the UART is going to be operating as
a sim of hardware, so information is the problem at the moment.

Google returns hundreds of explanations of the standard (now ITU-T
V.24 or EIA232) and this seems realistic:
http://www.camiresearch.com/Data_Com..._standard.html

The way I see it, there's a very simple way possibly...
A says "I'm ready to receive" over line 1, and B starts sending,
A says "I'm not ready to receive" over line 1, and B stops sending.
Invert A and B, communicate over line 2 and you have a primitive
full-duplex. However, if the only control lines you have are
RTS/CTS - which, from extra reading I've done, are for flow control
then I think I'm barking up the wrong tree. I'll have a look at the
sim code I think...

The problem is that in the spec, all the signals are part of the
protocol, and each implementation of hardware and software gets to
pick and choose which bits it will require, accept, or ignore.
Jumpering available signals to required signals normally solves the
problem, but it's often easier to jumper an available signal to all
the signals required by a particular interface.
Nine volt batteries and paper clips can be useful in emergencies.

--
Thanks. Take care, Brian Inglis Calgary, Alberta, Canada

Brian.Inglis (AT) CSi (DOT) com (Brian[dot]Inglis{at}SystematicSW[dot]ab[dot]ca)
fake address use address above to reply