Talk:RPi Serial Connection
I have confirmed that this adapter works with a synology TTL serial comm port. [] also confirmed the voltage is 3.3 from this convertor as loads of people were worried about degradation or failure using a 5v ttl serial convertor Waiting on the real thing to try it out.
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|Thread title||Replies||Last modified|
|USB serial connection to Raspian with systemd||0||15:36, 28 November 2017|
|Create a new page re: the manual configuration needed to prevent Linux from using the serial port||0||00:48, 20 May 2016|
|Glitch when serial port is opened||0||16:06, 25 July 2014|
The page was a little vague on how to do this with my version of Raspian. My uname -a:
- Linux raspberrypi 4.9.41-v7+ #1023 SMP Tue Aug 8 16:00:15 BST 2017 armv7l GNU/Linux
My system uses systemd. This is what ended up working for me:
- I plugged a USB to female crossover serial cable into the Raspberry Pi
- With my Arch Linux PC, I plugged in a USB to male serial straight-through and plugged that into the female of the Pi's crossover
- Verify the /dev/ttyUSB* port (it was /dev/ttyUSB0 for me) on the RPi. Then execute a serial getty in Raspian: systemctl start serial-getty@ttyUSB0.service (if you want it to start at boot, do systemctl enable serial-getty@ttyUSB0.service)
- From my Arch Linux PC I was able to connect with minicom -D /dev/ttyUSB1
It shouldn't really matter which host gets the straight through or which gets the crossover. However, if the PC has a serial port connected to its motherboard, you can plug the female end of the crossover directly into the PC's serial port and won't need another cable.
Just wanted to share in case this is helpful to someone else. I plan to use the built in serial port to control another device, but even if you don't this is a handy out of band connection to a RPi and/or lets you interact with your RPi's TTY console without a monitor and keyboard.
Create a new page re: the manual configuration needed to prevent Linux from using the serial port
I suggest to create a new page regarding the manual configuration needed to prevent Linux from using the serial port and place a link here because a) the text of that section is by far much longer than the other 2 methods b) almost everybody will use the other 2 methods and very-very few the manual one
When the serial port is opened there is a 32 us negative pulse on TXD (http://www.raspberrypi.org/forums/viewtopic.php?f=44&t=49867). Although many devices are error tolerant and thus not affected by this glitch, some are not and cannot easily be modified to deal with it. I would like to add a section to this page describing the glitch and how it can be avoided. It is difficult to search for information about this glitch. I did not find the linked forum post until I included 32us in the search string, and I only thought to measure the pulse because I was writing a new forum post myself. The glitch occurs when the serial port is opened, so the solution is to keep it open. This can be accomplished in bash with:
cat >/dev/ttyAMA0 &
If there are no objections I will add a small section on this glitch to this page in a few days.