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STR71x ADC Driving an Analog Keyboard

2 SOFTWARE CONFIGURATION

This software example manages the STR71x ADC configuration, and the key recognition

using the ADC software library.

After configuring the analog input as a high impedance analog input, the STR71x ADC has to

be enabled by setting the ADC_EN bit in the PCU_BOOTCR register. This action is followed

by selecting the Single Channel conversion mode and the Channel to be converted by setting

the AXT bit and writing the channel number in the A[1:0] bits in the Control Status Register

(ADC_CSR). Next, the prescaler has to be configured. Waiting for the availability of data in the

corresponding DATA register is done by looping on the Data Available flag (DAn) in

ADC_CSR register. After that, we can get the conversion result which will be calibrated.

The next step is the key recognition. This part of the software consists of testing if the conver-

sion result belongs to the range of the value of each key voltage. This range is defined by the

lower voltage (min [key]) and the higher voltage (max [key]) that are considered as corre-

sponding to the typical voltage of the key (Val [key]). This range is due to the resistor toler-

ance. Once the pressed key is recognized, its number is shown on four leds connected to

GPIO port 0 pins.

The main program is given by the next flowchart.