Serial Pi Plus not working

I am having difficulties getting the Serial Pi Plus working, allthough using the given instructions. I have the Raspberry Pi 3 B+. Serial Pi Plus is the only connected hardware.

I am running Rasbian with latest Updates and Upgrades.

Below is my setup.

/boot/cmdline.txt:

dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p7 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait splash plymouth.ignore-serial-consoles quiet

End of /boot/config.txt:

enable_uart=1

dtoverlay=pi3-miniuart-bt





In Raspberry configuration I have enabled the following interfaces:

SSH

Serial Port

Remote GPIO



The Serial Console is disabled



When doing the loopback test, connecting pins 2 & 3 in the DB9 and using either Putty or minicom with baud rate 9600 thru /dev/ttyS0, keystrokes are not echoed, nothing appears. I am doing this under sudo, so permissions shouldn’t be an issue. When connected to external device thru rs232 I can receive data but not able to send anything.



Are my settings correct?

Is there a way to debug the hardware to detect possible malfunction of the Serial Pi Plus?



Any advice on how to make the setup working?

Hi

Try commenting out the "enable_uart=1" line in the /boot/config.txt and use /dev/ttyAMA0 instead of ttyS0.

When you add the "dtoverlay=pi3-miniuart-bt" line to the /boot/config.txt it redirects the ttyAMA0 hardware UART port from the BlueTooth device to the UART pins on the GPIO header.

You may also need to disable hardware flow control in minicom for it to work correctly.

Hi Andrew,



thanks for the quick reply.

However, it didn't help. No change in the behaviour.

Any other tricks to try?

Try connecting the two UART pins together, pin 8 (GPIO 14) and pin 10 (GPIO 15) on the GPIO port without the serial pi plus connected. If the UART port is working then the keystrokes in minicom should be echoed, if not then that would suggest either a software or hardware problem with the Raspberry Pi.

If the UART port does echo the keystrokes then it could be a fault with the Serial Pi Plus and I will send you a replacement.

Hi Andrew,

the second loopback test failed as well.

So I took a fresh Pi from the shelf and started all from scratch. Now the loopback with Serial Pi Plus works, with the above proposed configurations.

Great!

Thanks a lot for the support.