ST52T301 datasheet(28/100 Pages) STMICROELECTRONICS

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6. A/D CONVERTER

The A/D Converter of ST52x301 is an 8-bit analog

to digital converter with up to 4 analog inputs

offering 8 bit resolution with a total accuracy of 2

LSB and a typical conversion time of 32

µs.

The conversion range is 0 - 2.5 V.

The A/D peripheral converts the input voltage with

a process of successive approximations using a

fixed clock frequency derived from the oscillator.

The ADC uses 5 registers: one Configuration

These 4 registers are the first 4 Input Registers.

The A/D converter drives the analog Multiplexer in

order to sequentially pick up the external inputs to

be put in output and stored automatically in 4 8-bit

registers.

It is possibile to configurethe Multiplexer by means

of the register REG_CONF2, in order to select the

number of analog inputs to convert.

For example, if the bit 3 and bit 2 of REG_CONF2

are configured at 10, then the Multiplexer will

sequentially pick up only the inputs 0,1 and 2.

Tab le 6.1 shows the conver tion sequences

according to the possible values of the two bit

REG_CONF2 (3:2).

The A/D Converter, at the end of the conversion,

will send a signal (end-of-conversion)which can be

used like an interrupt signal. The user can select

the priority of the A/D interrupt and mask it (see

”Interrupt Routine” chapter)

Th e

co nve rs io n

s ta r t s

w rit i ng

”1”

REG_CONF2(0). The A/D is reset by writing ”0” in

REG_CONF2(0).

The converted data are automaticallystored in four

8-bit Input Registers.

By performing an instruction:

LDRI regj ingi

the analog input ”ingi” is loaded in the register”regj”

of the Register File.

Figure 6.1. A/D Converter Structure

CONF_REG2 (3:2)

INPUT SEQUENCE

Ain0

Ain 0, Ain1

Ain 0, Ain 1, Ain 2

Ain 0, Ain 1, Ain 2, Ain 3

Table 6.1.

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