[PLUG] serial communication with dmm (was com port in guest to usb in host (virtual box))

Tomas Kuchta tomas.kuchta.lists at gmail.com
Fri Dec 29 23:36:59 UTC 2017


I have one of those simple Bitscope scopes/analysers for slow RPi type
interface hacking it might be the right tool for the job and it runs on
Linux.

Would that help? Do you want to borrow it?

Check the Bitscope website for details, but it is good enough for serial
ports. Perhaps even decoding it.

Tomas

On Dec 29, 2017 2:44 PM, "Denis Heidtmann" <denis.heidtmann at gmail.com>
wrote:

> I made the measurements with my 'scope.  The voltages and waveforms are
> identical comparing  DTR, RTS (also RXD), although I am surprised a little
> that the pulses on DTR are as large as they are: 2.4V swing.  Must be some
> resistance in the supply to the drain.  But the level is up at 11.6V, so
> those 2.4V drops cannot matter.  The signals on the RXD pin are -3.6 to
> +8.2V for both the mfg. sw and sigrok.
>
> So no explanation yet, and hence no solution.  Is there a way to examine
> the serial parameters the mfg. sw uses?  Perhaps the docs on the protocol
> are in error.
>
> On Fri, Dec 29, 2017 at 9:17 AM, Denis Heidtmann <
> denis.heidtmann at gmail.com>
> wrote:
>
> > I will make those measurements, but I am doubtful it will show anything.
> > The schematic I have shows DTR to be the collector and RTS to be the low
> > end of the emitter resistor of the output NPN.  I did see solid pulses on
> > the emitter with sigrok.  But perhaps DTR and/or RTS are pulsed when they
> > should not be.  It is too bad my 'scope has limited record length and no
> > way to store the data off the 'scope.
> >
> > On Thu, Dec 28, 2017 at 11:42 PM, Russell Senior <
> > russell at personaltelco.net> wrote:
> >
> >> Have you measured the voltages on DTR and RTS during the runs?
> >>
> >> Try it with sigrok and with the vendor software and see if there is a
> >> difference in those values.
> >>
> >> On Thu, Dec 28, 2017 at 9:51 PM, Denis Heidtmann
> >> <denis.heidtmann at gmail.com> wrote:
> >> > This saga continues.
> >> >
> >> > On the laptop with a usb-serial adapter I got to the point where the
> >> > commands:
> >> > sigrok-cli --driver mastech-mas345:conn=/dev/ttyUSB0 --show
> >> > sigrok-cli --driver mastech-mas345:conn=/dev/ttyUSB0 --scan
> >> > sigrok-cli --driver mastech-mas345:conn=/dev/ttyUSB0 --samples 10
> >> >
> >> > behave as expected except the last one returns no data.  I was advised
> >> to
> >> > try using these same commands on the desktop which has an RS232 port,
> >> thus
> >> > removing the usb-serial adapter from the picture.  Good idea.
> >> >
> >> > After just guessing what serial port to use, I run the following
> >> command:
> >> >
> >> > sigrok-cli --driver mastech-mas345:conn=/dev/ttyS0 --scan
> >> > The following devices were found:
> >> > mastech-mas345 - MASTECH MAS345 with 1 channel: P1
> >> >
> >> > This is the same response I got on the laptop.
> >> >
> >> > sigrok-cli --driver mastech-mas345:conn=/dev/ttyS0 --show
> >> > mastech-mas345 - MASTECH MAS345 with 1 channel: P1
> >> > Supported driver options:
> >> >     conn
> >> >     serialcomm
> >> > Supported configuration options:
> >> >
> >> > This is the same response I got on the laptop.
> >> >
> >> > sigrok-cli --driver mastech-mas345:conn=/dev/ttyS0 --samples 10
> >> >
> >> > [no response except the usual ~10 second delay]
> >> >
> >> > This is the same response I got on the laptop.  RATS!
> >> >
> >> > This eliminates the usb-serial device from the picture.
> >> >
> >> > Recall that when running --samples 10 command on the laptop I was able
> >> to
> >> > detect pulses on the serial line consistent (in a general sense) with
> a
> >> > response from the dmm.  Also recall that running  the mfg. sw under
> >> windows
> >> > on the desktop showed flawless communication.
> >> >
> >> > finally, I report:
> >> > stty -F /dev/ttyS0 -a   speed 600 baud; rows 0; columns 0; line = 0;
> >> > intr = <undef>; quit = <undef>; erase = <undef>; kill = <undef>; eof =
> >> > <undef>;
> >> > eol = <undef>; eol2 = <undef>; swtch = <undef>; start = <undef>; stop
> =
> >> > <undef>;
> >> > susp = <undef>; rprnt = <undef>; werase = <undef>; lnext = <undef>;
> >> > discard = <undef>; min = 0; time = 0;
> >> > -parenb -parodd -cmspar cs7 hupcl cstopb cread clocal -crtscts
> >> > -ignbrk -brkint ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl
> -ixon
> >> > -ixoff
> >> > -iuclc -ixany -imaxbel -iutf8
> >> > -opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0
> >> bs0
> >> > vt0 ff0
> >> > -isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase
> -tostop
> >> > -echoprt
> >> > -echoctl -echoke -flusho -extproc
> >> >
> >> > And the protocol is reported to be:
> >> >
> >> > data format: 7n2 at 600 baud (7 bits, no parity, 2 stop bits).
> >> > Control lines:
> >> >    DTR and RTS lines are used to power the TX line: RTS is clear
> >> >    for -12 supply; DTR is set for +12 supply. Data transmission is
> >> >    solicited sending whatever character to the RX line.
> >> >
> >> > Any suggestions as to where to go from here?
> >> >
> >> > Thanks,
> >> > -Denis
> >> > _______________________________________________
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> >
> >
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