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STR71x ADC Driving an Analog Keyboard

interrupt will be generated if all interrupt bits and all Data Available flags in the ADC_CSR are

set.

The clock configuration of the STR71x converter is used to define the oversampling fre-

quency which clocks the modulator of the Sigma-Delta converter. This frequency is pro-

is obtained by configuring the 12-bit value of the prescaler register.

The value to write in the Converter prescaler register is:

ADC_CPR = (RCCU_FrequencyValue(RCCU_PCLK)/(Adc12_clk*512*8))

The real factor, by which the input frequency will be multiplied to produce the oversampling

frequency, is twice the prescaler register value.

1.2 I/O CONFIGURATION

The STR71x Analog to Digital Converter provides four analog input pins for connecting dif-

ferent analog signals. These pins are internally multiplexed to use the same Sigma-Delta

logic.

Depending on the conversion mode (Continuous or Single Channel), you can use either the

four analog inputs or only one selected pin. If you are using the Single Channel mode, you can

select a pin by writing the channel number in the A[1:0] bits in the Control Status Reg-

ister(ADC_CSR). These pins are mapped on the pins of GPIO port 1(P1.1, P1.2, P1.3, P1.4).

To use the port pins as analog inputs, you must configure them as High impedance-Analog In-

puts by writing the appropriate values in to the PC0, PC1 and PC2 registers of GPIO Port 1.

1.3 ANALOG KEYBOARD

The analog keyboard is formed by a number of keys connected to resistive dividers; with a

pull-up resistor. In the analog keyboard each key is associated with a voltage.

R0-->R14: serial resistors through which keys will be connected to the analog input.

key0

key1

key14

key15

Keyboard

To Analog input