[PLUG] com port in guest to usb in host (virtual box)

[Russell Senior]

The precise levels are not supposed to make a difference.  Below a
negative threshold and above a positive threshold should be enough.
>From memory, original RS232 was +/- 12V, but any remotely modern PC
would use +/- 5V-ish.

  https://en.wikipedia.org/wiki/RS-232#Voltage_levels

What happens to DTR and RTS when using sigrok?

-- 
Russell

On Wed, Dec 13, 2017 at 7:54 PM, Denis Heidtmann
<denis.heidtmann at gmail.com> wrote:
> To step back a bit I fabricated a little fixture to make it convenient to
> test the lines going into the dmm. I found a description of those lines:
> 5-pin inline connector.
>
> pin 1 Gnd
> pin 2 TX
> pin 3 RTS (must be off)
> pin 4 DTR (must be on)
> pin 5 RX
>
> The connections are through optical couplers in the meter, hence the "must
> be" conditions. Pin 2 connects to the anode of the led of the input
> coupler, pin 3 is connected to the emitter of the output npn through a
> resistor, pin 4 connects to the collector of the output npn, and pin 5
> connects directly to the emitter of that npn.
>
> I ran (what I presume is the vendor's sw) in a VB windows 2000 guest on my
> desktop (Lenovo ThinkCentre M92P), which has an RS232 port.  The sw
> communicates with the dmm fine.  I checked the voltages wrt Gnd:
>
> Pin 2 -10 (the meter I used did not detect the signal - I need to use a
> 'scope to see what the signal actually is)
> pin 3 -9.5 to -10
> pin 4 +10 to +10.8 on line; -10V off line.
> pin 5 data
>
> When I was examining this with the laptop and the usb-to-serial adapter I
> saw voltages no higher than 6.4V.  It is possible that explains the lack of
> response from the meter, although the sigrok --scan and --show commands did
> find the meter.  I do not know how the meter could be identified without
> valid communication.
>
> So this is the status.  I will check the voltages when connected to the
> laptop, and drag out the 'scope to see what I can learn.
>
> On Mon, Dec 11, 2017 at 12:28 PM, Russell Senior <russell at personaltelco.net>
> wrote:
>
>> On Mon, Dec 11, 2017 at 11:21 AM, Denis Heidtmann
>> <denis.heidtmann at gmail.com> wrote:
>> > Is it possible that your command /dev/ttyUSB0 600,cs7,cstopb,-parenb has
>> an
>> > error?
>>
>> Not only possible, but likely.
>>
>> > I executed stty 600 then stty -a :
>> > denis at denis-ThinkPad-L420:~$ stty -a
>> > speed 600 baud; rows 24; columns 80; line = 0;
>> > intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
>> > eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt
>> =
>> > ^R;
>> > werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;
>> > -parenb -parodd -cmspar cs8 -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
>> >
>> > Then I tried stty cs7 and got:
>> > denis at denis-ThinkPad-L420:~$ stty cs7
>> > stty: 'standard input': Invalid argument
>> >
>> > Yet the man page lists csN.
>> >
>> > Clearly I do not know what I am doing.
>>
>> You probably need to tell it which tty you want to talk to, otherwise
>> it will try to set your current terminal, afaik.
>>
>> The device-busy thing may be due to a screen session still running.
>> Try unplugging/replugging your cable from the USB port.
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