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DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC

F (PF0, PF4), and Port C (PC0, PC1, PC5, PC7). The I/O port pins used by the ADC must be

configured as floating inputs to avoid conflicts in alternate function mode.

Refer to the Data Sheet for information on configuring the I/O ports.

3.2 ANALOG TO DIGITAL CONVERTER

The ST7 ADC is a 10-bit successive approximation converter, with internal sample and hold-

circuitry.

3.2.1 ADC control

You control the ADC using the ADC Control Status Register (ADCCSR).

The EOC bit is the end of conversion bit:

- When this bit is set, the conversion is done and result can be read from the ADC

Data Registers (ADCDRL & ADCDRH).

- When the bit is reset, the conversion is not complete.

The SPEED bit:

The ADON bit:

- Enable ADC and start conversion when this bit is set.

- Disable ADC and stop conversion when this bit is reset.

CH3-CH0 bits:

- They are used to select which analog input to convert. In the ST72324 there are 12

analog pins.

3.2.2 Characteristics

The conversion time is 15 ADC cycles including a sampling time of 4 ADC cycles.

The ADC is linear and the digital result of the conversion is given by the formula:

Digital Result =

3.2.3 Process

First the analog input pins must be configured as floating inputs (see Section 3.1).

CH0

CH1

CH2

CH3

0

ADON

SPEED

EOC

1023*Input Voltage

Reference Voltage