Re: minicom serial output
From: anonymous coward (anonymous.coward_at_nospam.nowhere)
Date: Thu, 22 Jul 2004 02:40:56 +0100
On Wed, 21 Jul 2004 10:17:35 -0800, Floyd L. Davidson wrote:
> anonymous coward <firstname.lastname@example.org> wrote:
>>On Wed, 21 Jul 2004 05:58:42 -0800, Floyd L. Davidson wrote:
>>> anonymous coward <email@example.com> wrote:
>>> [background info snipped]
>>>>I've been trying to get them to work using minicom. I've set the correct
>>>>data rate, flow control settings etc. etc. but minicom only seems to work
>>>>in one direction. It will print data from my electronics, but it will
>>>>not echo what I type into the keyboard into my electronics.
>>>>If I try to start a modem, my electronics reacts to the control sequences
>>>>so there does not seem to be any hardware problem.
>>>>Any ideas? I'm sure I'm doing something pretty basic wrong, but I have no
>>> I'm not sure that I understand your description. Are you saying
>>> that when you type something on the keyboard, the device you
>>> have connected to the serial port *does* react? Meaning that it
>>> has received the data?
>>Sorry - I can see my original question wasn't very clear. My device
>>doesn't react and a multimeter accross the serial port shows that no data
>>was transmitted from the computer to the device.
>>I can tell that the input to the computer is working because my device
>>shows a 'welcome' message as it boots up. It also reacts to the modem
>>initialisation / hangup commands. These are sent correctly which I imagine
>>shows that there is no hardware or permissions problem - i.e. I can write
>>to the serial port.
>>> So "I try to start a modem" means that you used minicom's "Initialize
>>> Modem" command and it sent something the device responded to... you
>>> want to configure minicom to *not* send it!
>>Yes, that's correct. I already changed the modem initialisation string to
>>'D' (one of the commands recognised by my device) and I can get my device
>>to respond sensibly to this command whenever I initialise the modem. But
>>I have many more commands, and at the moment if I wish to switch between
>>commands I have to change the modem init string each time, hangup... It's
>>What I'd like to be able to do, would be to type the commands directly
>>into the terminal and have them sent out to the serial port.
> At this point I am simply unable to explain what you just
> described! Your analysis of what it means is good. But my
> understanding of what minicom does cannot match what you
> If you can see the welcome message from your device, then we can
> assume that basically you do indeed have the port configured
> either correctly, or at least close enough to show some signs of
> If you can send a command to it using the modem init capability
> of minicom and see the reaction to it, I simply do not know why
> you could not then send a second command from the keyboard.
> There are a couple of (remotely) possible ways that you just
> haven't tried in exactly the right combination to show what is
> happening, but given your descriptions I'm not inclined to think
> you are jumping to conclusions! Regardless, let me discuss a
> couple possible stumbing blocks that might be overlooked by
> someone who isn't experienced with data comm.
> If you get the parity setting wrong, some characters work and
> some don't. So you might find that 1 out of 5 different
> commands typed in would get a response. It sounds like you've
> tried enough things that you would have mentioned those symptoms
> if they were being displayed.
Nothing is being sent to the serial port - with either correct or
incorrect parity. I'm using a very slow data rate (300bps) so I can
always see a 'glitch' on my multimeter if something is transmitted.
I have also tried sending strings that would be sure to show up.
Each command is a single byte long - if invalid commands are received the
device says so, but does not hang so the problem can't be to do with hash
> Another odd one is how each line is terminated, and this is
> indeed something which could be tripping you up. Try sending
> lines terminated with ^M^J and others terminated with ^J^M.
> Past that, and those don't look promising, I just don't see why
> it would not work as you are expecting. I have used minicom to
> talk to dozens or even hundreds of devices, and you are
> certainly describing the right approach.
My device is very simple and only uses ground, TD and RD. All the other
lines are left floating. I wonder whether this could be part of the
problem, even though I turned off both software handshaking and
> It doesn't sound as if either the hardware (cabling) or the port
> configuration could be a cause. It appears to have something to
> do with the way the terminal and/or the init strings for minicom
> are configured.
> One thing you might do is find a handy old modem that has LEDs
> to indicate various states, including TxD and RxD. Then you
> can actually see when data is being sent. Hook the modem up
> and see if you can talk to it. If not, it will probably be
> a lot easier to see what is or not happening with the modem
> than with any other device. If it does *not* work with your
> present minicom configuration, go back to the default configuration
> and change that one step at a time until you find something that
> causes it to stop working. If it does work as currently configured,
> then you probably do have a port configuration problem (because the
> modem just adapts to whatever your send parameters are, and your
> device probably does not).
> Keep us posted! Especially if you find a fix. (Don't be
> embarassed either, because *all* problems are simple *after* the
> fact! There is nothing you can have done that is half as dumb
> as things I've done more than once... :-)
I will do - though I can't investigate too deeply at the minute (time