SerialPorts < IoT_Course

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---+ Using a second Serial Port

On the ESP32 UART0 is normally reserved for interactive use with REPL. Sometimes we need a !UART to communicate with external devices. Typical examples are:
   * fingerprint readers using a serial communication protocol
   * GPS modules
The ESP32 has 3 !UARTs of which however UART1 is reserved for use with flash memory. <b>However, UART2 is free. <br /></b>Normally Rx is connected to GPIO 16 and Tx to GPIO 17 but these are forbidden on the CPU card we use (see [[The hardware]]). It is possible however to remap these signals to different GPIO pins, in our case to GPIO 21 and 22.

Connect the USB to Serial adapter to the ESP32 as shown in the table below

|  USB to Serial Adapter  |  ESP32 pins  |
|  Rx  |  GPIO 21  |
|  Tx  |  GPIO 22  |
|  Gnd  |  Gnd  |
As a first quick test, we can try to write "Hello World to UART2 to which we connect a minicom virtual terminal.

_thonny_ is connected to UART0 on /dev/ttvUSB0 (connect this first). <i>minicom </i>is connected to UART2 on /dev/ttyUSB1. Start minicom with:

_minicom -D /dev/ttyUSB1_

Here is the screen dump of the REPL session

<img alt="uart2-v2.png" height="176" src="%ATTACHURL%/uart2-v2.png" title="uart2-v2.png" width="746" />

And this is what we see on minicom:

<img alt="uart2-minicom.png" height="209" src="%ATTACHURL%/uart2-minicom.png" title="uart2-minicom.png" width="559" />

... if you are too lazy to type, here is the corresponding script:

%ATTACHURL%/uart.py.txt

-- %USERSIG{UliRaich - 2020-05-09}%
---++ Comments

%COMMENT%

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
txt	uart.py.txt	r1	manage	0.2 K	2020-05-09 - 20:01	UliRaich
png	uart2-minicom.png	r1	manage	23.7 K	2020-05-09 - 19:57	UliRaich
png	uart2-v2.png	r1	manage	26.9 K	2020-10-12 - 15:42	UliRaich
png	uart2.png	r2 r1	manage	26.9 K	2020-10-12 - 15:40	UliRaich

Topic revision: r2 - 2020-10-12 - UliRaich