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pi 3 - Unable to read the RS232 attached GPIO pins the same way as USB serial port on Pi3 - Raspberry Pi Stack Exchange
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Activate the TTL serial port of the Raspberry Pi and verify that it is working. – Howto Raspberry Pi
![Activate the TTL serial port of the Raspberry Pi and verify that it is working. – Howto Raspberry Pi Activate the TTL serial port of the Raspberry Pi and verify that it is working. – Howto Raspberry Pi](https://raspberry-pi.fr/wp-content/uploads/2020/07/connexion_serie_test-939x528.jpg)
Activate the TTL serial port of the Raspberry Pi and verify that it is working. – Howto Raspberry Pi
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