ST9 datasheet(67/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

– Analog Input (see note)

Note:

On the port that accommodates the inputs of the Analog to Digital Converter, there is a special

feature. In all other peripherals that require an input, you only need to configure the correspond-

ing pin as an input. However, when using the ADC you can put the input pins to any voltage level

from ground to Vcc. This is normally badly handled by standard logic gates that dissipate con-

siderable power when the voltage reaches the limit range. To avoid this, the port that provides

the input pins of the ADC has a special Alternate Function mode. Unlike the other ports it is used

for input. This mode disconnects the input buffer from the pin and shorts the buffer input to the

ground. The output buffer is put in high-impedance mode. The pin is permanently connected to

the input of the ADC, thus allowing its voltage to be read at any time.

To handle all these capabilities, each port requires three configuration registers, PxC1, PxC2

and PxC3, where x is the port number. Once configured, a port exchanges data with the core

through the PxDR data register.

The configuration registers are placed in various pages of the register group 15, as well as the

data registers, except for the first six ports. These six belong to the system register group

(group 14) for easy access.

Some ports also include DMA capability, configurable to work with the Multi-Function Timer.

ST9 数据表(PDF) 67 Page - STMicroelectronics