Rainbow-electronics ADC0848 Bedienungsanleitung PDF herunterladen (Seite 8)

Functional Description

The ADC0844 and ADC0848 contain a 4-channel and 8-

channel analog input multiplexer (MUX) respectively. Each

MUX can be configured into one of three modes of opera-

tion differential, pseudo-differential, and single ended.

These modes are discussed in the Applications Information

Section. The specific mode is selected by loading the MUX

address latch with the proper address (see Table I and Ta-

ble II). Inputs to the MUX address latch (MA0-MA4) are

common with data bus lines (DB0-DB4) and are enabled

when the RD

line is high. A conversion is initiated via the CS

and WR lines. If the data from a previous conversion is not

read, the INTR

line will be low. The falling edge of WR will

reset the INTR

line high and ready the A/D for a conversion

cycle. The rising edge of WR

, with RD high, strobes the data

on the MA0/DB0-MA4/DB4 inputs into the MUX address

latch to select a new input configuration and start a conver-

sion. If the RD

line is held low during the entire low period of

the previous MUX configuration is retained, and the

data of the previous conversion is the output on lines DB0-

DB7. After the conversion cycle (t

40 ms), which is set

by the internal clock frequency, the digital data is trans-

ferred to the output latch and the INTR

is asserted low.

Taking CS

and RD low resets INTR output high and outputs

the conversion result on the data lines (DB0-DB7).

Applications Information

1.0 MULTIPLEXER CONFIGURATION

The design of these converters utilizes a sampled-data

comparator structure which allows a differential analog input

to be converted by a successive approximation routine.

The actual voltage converted is always the difference be-

tween an assigned ‘‘

’’ input terminal and a ‘‘

’’ input ter-

minal. The polarity of each input terminal of the pair being

converted indicates which line the converter expects to be

the most positive. If the assigned ‘‘

’’ input is less than the

‘‘

’’ input the converter responds with an all zeros output

code.

A unique input multiplexing scheme has been utilized to pro-

vide multiple analog channels. The input channels can be

software configured into three modes: differential, single-

TABLE I. ADC0844 MUX ADDRESSING

MUX Address

WR RD

Channel

MUX

MA3 MA2 MA1 MA0 CH1 CH2 CH3 CH4 AGND Mode

XLLLL H

XLLHL

Differential

XLHLL H

XLHHL H

LHLLL H

LHLHL

Single-Ended

LHHLL H

LHHHL H

HHL LL H

Pseudo-

HHLHL£H

Differential

HHHLL H

XXXXL£L Previous Channel Configuration

don’t care

4 Single-Ended

TL/H/5016–12

2 Differential

TL/H/5016–13

3 Pseudo-Differential

TL/H/5016–14

Combined

TL/H/5016–15

FIGURE 1. Analog Input Multiplexer Options

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 19 20

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