5.2 Base Station Application for the SAMC21 MCU

The following figure illustrates the program flow for the SAMC21 application. This application performs initialization of the peripherals (GPIOs, USART and SPI), the LEDs and the OLED display. The ATA5831 RF transceiver is switched into RF Polling mode to check for the reception of a valid Remote Sensor signal. In addition, the base station initializes a timer for time measurements between RF signal transmissions. The software, then, enters into an infinite loop to check for an RF event signal from the RF transceiver or for a button press of one of the buttons on the OLED1-XPRO extension board. A button press shows the corresponding information on the OLED display (see the following figure). When the base station detects an RF event, the RX and RSSI buffer are read and the RX data are checked with their checksum to be a valid data stream. If the data is not valid, the base station enables the Polling mode to check for another RF signal. If the data is valid, the base station sends an acknowledgment telegram and waits for an RF answer telegram. At last, the OLED display shows the received temperature and RSSI data. All the text on the OLED display is also streamed via the USART peripheral, and the user can see the same on the PC terminal program connected to the virtual COM port of the ATSAMC21-XPRO evaluation kit.

Figure 5-2. Flash Application for the SAMC21 MCU

The OLED display shows the following information:

Start page – Displays the welcome message with software and transceiver firmware version information and awaits a Remote Sensor signal
```
ATA8510-EK1 Demo Kit
(c)2022 Microchip V4.0 
waiting for RF signal
.....
```

Button 1 menu – Displays RF signal characteristics

RF-Channel 433.92MHz 
Data rate 8kBit/s 
FSK deviation +/-8kHz 
Manchester coding

Button 2 menu – Displays parameters used for the virtual COM port. These parameters must be set in the PC terminal application to receive the text strings.
```
COM port settings 
baudrate 38.4kBaud
8 data + 1 stop bit
no parity, no handshake
```

Button 3 menu – Displays receiver packet statistics
```
Receiver statistics: 
valid# 3062
error# 15
total# 3099
```

Measurement results – The measurement display shows the time interval dt between two consecutive RF telegram receptions together with the RSSI value for the RF signal strength at the base station and at the remote sensor. The temperature at the sensor is shown with a resolution of 1°C.

If there is an error, the OLED displays the following error messages:

When the received data telegram is corrupted or when the temperature sensor is broken or not present
```
!!!!!!!!!!!!!!!!!!!!!!
Sensor error:
Invalid sensor data!
!!!!!!!!!!!!!!!!!!!!!!
```
When the sensor battery has a voltage below 2.2V and there is a need for replacement
```
!!!!!!!!!!!!!!!!!!!!!!
Sensor error:
Low battery voltage!
!!!!!!!!!!!!!!!!!!!!!!
```
When the base station receives a wrong acknowledgment telegram
```
::::::::::::::::::::::
RF telegram error:
Wrong ACK telegram!
::::::::::::::::::::::
```
When the base station does not receive an RF acknowledgment telegram
```
::::::::::::::::::::::
RF channel error:
No RF ACK telegram!
::::::::::::::::::::::
```
When the base station cannot send an RF acknowledgment telegram
```
::::::::::::::::::::::
RF channel error:
RF TX telegram err!
::::::::::::::::::::::
```
When the RF receiver is detecting a signal on another RF channel
Note: Enable the signal in the EEPROM configuration of the receiver.
```
::::::::::::::::::::::
RF channel error:
Wrong RF telegram!
::::::::::::::::::::::
```