ADC08231CIWM datasheet(15/24 Pages) NSC

15 / 24 page

Functional Description (Continued)

Since the input configuration is under software control it

can be modified as required before each conversion A

channel can be treated as a single-ended ground refer-

enced input for one conversion then it can be reconfigured

as part of a differential channel for another conversion

Fig-

ure 1 illustrates the input flexibility which can be achieved

The analog input voltages for each channel can range from

50mV below ground to 50mV above VCC (typically 5V) with-

out degrading conversion accuracy

20 THE DIGITAL INTERFACE

A most important characteristic of these converters is their

serial data link with the controlling processor Using a serial

communication format offers two very significant system im-

provements it allows many functions to be included in a

small package and it can eliminate the transmission of low

level analog signals by locating the converter right at the

analog sensor transmitting highly noise immune digital data

back to the host processor

To understand the operation of these converters it is best to

refer to the Timing Diagrams and Functional Block Diagram

and to follow a complete conversion sequence For clarity a

separate timing diagram is shown for each device

1 A conversion is initiated by pulling the CS (chip select)

line low This line must be held low for the entire conver-

sion The converter is now waiting for a start bit and its

MUX assignment word

2 On each rising edge of the clock the status of the data in

(DI) line is clocked into the MUX address shift register

The start bit is the first logic ‘‘1’’ that appears on this line

(all leading zeros are ignored) Following the start bit the

converter expects the next 2 to 4 bits to be the MUX

assignment word

8 Single-Ended

8 Pseudo-Differential

4 Differential

Mixed Mode

TLH11015 – 17

FIGURE 1 Analog Input Multiplexer Options for the ADC08238

ADC08231CIWM bảng dữ liệu(PDF) 15 Page - National Semiconductor (TI)