Stratcat
Posts: 9
Joined: Wed Jan 16, 2019 9:45 am

RS232 without using GPiO help please?

Sat Feb 09, 2019 4:33 pm

Hi this my first post.

I have been reading up a lot on the RPi but find haven't found a clear answer or a sticky guide for new Pi users like me.

I want to be able to use keyboard and mouse to a pi via the normal usb ports with display hooked to hdmi. So nothing different there. Once I have that I want to use something like PuTTY on the pi to talk RS232 to another RS232 device.

I am aware that the gpio is only safe for 3.3V being fed to it from another device. So I am trying to Avoid using the gpio uart.

I have one of these ;

https://www.amazon.co.uk/VTOP-Serial-RS ... pter+cable

Firstly will this work safely with the pi using USB at the pi end and 9 way pins for the other device to be communicated with?

Secondly if the answer to the first question is yes, would that cable be seen as another TTY port by the pi so that the gpio does not need to be disabled?

Thank you.
Phil

klricks
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Location: Grants Pass, OR, USA
Contact: Website

Re: RS232 without using GPiO help please?

Sun Feb 10, 2019 3:56 am

Stratcat wrote:
Sat Feb 09, 2019 4:33 pm
......
Firstly will this work safely with the pi using USB at the pi end and 9 way pins for the other device to be communicated with?

Secondly if the answer to the first question is yes, would that cable be seen as another TTY port by the pi so that the gpio does not need to be disabled?

According to some of the product reviewers this device works on RPi.
If you are not going to use the GPIO UART then you don't need to disable Linux console or do anything else.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

tpyo kingg
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Joined: Mon Apr 09, 2018 5:26 pm
Location: N. Finland

Re: RS232 without using GPiO help please?

Sun Feb 10, 2019 6:32 am

It is the chipset in the adapter which is relevant for support. That cable uses the PL2303 and that is well supported. If you plug it in, you can look at the information it provides to the system:

Code: Select all

lsusb | less
lsusb -v | less
Scroll down to where it says "Prolific Technology, Inc. PL2303 Serial Port"

tempest766
Posts: 105
Joined: Sun Jan 07, 2018 3:44 pm

Re: RS232 without using GPiO help please?

Sun Feb 10, 2019 8:38 am

you should be good. All you really need to understand at this point is whether it is a DTE-DCE or DTE-DTE connection you are tyring to make; firt being a terminal to a modem, and the second being a terminal to terminal. which lines need switched and how flow control is handled are the specifics. It should should up as /dev/ttyUSB? on the pi. I believ that usb serial converter chip is well supported in linux.

Stratcat
Posts: 9
Joined: Wed Jan 16, 2019 9:45 am

Re: RS232 without using GPiO help please?

Sun Feb 10, 2019 7:15 pm

Thank you very much for the rapid replies to enquiry. The additional linux commands 'lsusb' and 'less' will help too as although I'm not new to computers and coding my background has been raw assembler code for a variety of cpus.

The idea is to use a Pi zero as an old fashioned computer terminal in place of a laptop. The 'terminal' is to communicate with a home made synthesizer that an old school friend is designing and building. We're both getting on a bit and find getting to grips with operating system level stuff and terminalogy (forgive the pun) a bit confusing.

Thank you again.
Phil

tempest766
Posts: 105
Joined: Sun Jan 07, 2018 3:44 pm

Re: RS232 without using GPiO help please?

Sun Feb 10, 2019 9:03 pm

Stratcat wrote:
Sun Feb 10, 2019 7:15 pm

The idea is to use a Pi zero as an old fashioned computer terminal in place of a laptop. The 'terminal' is to communicate with a home made synthesizer that an old school friend is designing and building. We're both getting on a bit and find getting to grips with operating system level stuff and terminalogy (forgive the pun) a bit confusing.
been there. done that. I'm kicking myself for giving away a well working DEC VT131 a few years ago. times I just need a dumb terminal without "configuring" a PC to do the task.

Stratcat
Posts: 9
Joined: Wed Jan 16, 2019 9:45 am

Re: RS232 without using GPiO help please?

Mon Feb 11, 2019 1:32 pm

:D And how many years did you survive being told 'can't you get rid of that clutter....'

I hate to think how much stuff has gone that way over the years.

On a note to who it was that mentioned DTE etc. We only need 3 wire grnd, rx and tx and can use xon/xoff if needed in the synth firmware.

What is the best reference for how linux identifies and updates attached hardware like the usb serial port?

Kind regards
Phil

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rpdom
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Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: RS232 without using GPiO help please?

Mon Feb 11, 2019 1:43 pm

tempest766 wrote:
Sun Feb 10, 2019 9:03 pm
I'm kicking myself for giving away a well working DEC VT131 a few years ago. times I just need a dumb terminal without "configuring" a PC to do the task.
I still have a Wyse 60 terminal that does VT emulation. I have linked it up to a Pi at one point.
Signature is on holiday.

tempest766
Posts: 105
Joined: Sun Jan 07, 2018 3:44 pm

Re: RS232 without using GPiO help please?

Mon Feb 11, 2019 6:50 pm

Stratcat wrote:
Mon Feb 11, 2019 1:32 pm
On a note to who it was that mentioned DTE etc. We only need 3 wire grnd, rx and tx and can use xon/xoff if needed in the synth firmware.

What is the best reference for how linux identifies and updates attached hardware like the usb serial port?
at least you said "3 wire" and didn't do the "we don't need no stinking ground" answer. and it is nice that you know what flow control is. :lol:

"best reference" is a hard concept in the internet collaberative world, as IMHO there is very little quality documentation for anything developed as an internet collaberative project.

the short answer is that USB devices have driver classes, in this case serial device class. the vendor/product ID in the device tells the linux kernel that it is a serial device and which vendor driver to load. if they did it right then the vendor driver creates the next possible enumerated device as /dev/ttyUSBn. you can force a different device name by editing the udev rules; a hook where the device driver tells the kernel that vendor x, product y has been insterted. at that point udev can create a device file entry based on special rulesets. google udev for details.

Stratcat
Posts: 9
Joined: Wed Jan 16, 2019 9:45 am

Re: RS232 without using GPiO help please?

Tue Feb 12, 2019 8:52 pm

:D Glad I'm considered a level up.... for knowing the necessity of using ground, it goes with a UK class 'A' radio licence and a goodly while playing with electronics, chemistry, computers, guitars and motorcycles. My synth school mate is somewhat similar only far more electronics guru working on electronics for lasers that can draw circles (sort of) of C. 1 angstrom diameter for the chip industry.

It is really quite sad that I have to agree with your views on 'open development and internet sharing' I do find more often than not that using the internet and most notably tech support pages that it is a long winded case of sifting the wheat from the chaff, lord alone knows its tough enough but when duff information remains posted it just obscures and undermines the trust in the real useful stuff.

I would personal mail you as I don't want to fill up the thread with chat per se, but I don't think we can on here so I'll keep an eye out for your posts.
Kind regards

tempest766
Posts: 105
Joined: Sun Jan 07, 2018 3:44 pm

Re: RS232 without using GPiO help please?

Tue Feb 12, 2019 9:40 pm

yeah. the contact function seems to be inactive.

I'm a Buell guy. Have a 2008 Uly-xt, and grew up in the same county as Eric Buell. A couple years ago switched to a 2015 Yammee FJR, but keep the Uly running as a hooligan bike. Look up Kent Dorfman on facebook and find the image of the baby smoking the cigar and holding the bottle of Jack.

Cheers

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