ADC0833 datasheet(10/20 Pages) NSC

10 / 20 page

Functional Description (Continued)

Since the input configuration is under software control it

can be modified as required at each conversion A channel

can be treated as a single-ended ground referenced input

for one conversion then it can be reconfigured as part of a

differential channel for another conversion

Figure 1 illus-

trates the input flexibility which can be achieved

The analog input voltages for each channel can range from

50 mV 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 more function to be included in the

converter package with no increase in package size and it

can eliminate the transmission of low level analog signals by

locating the converter right at the analog sensor transmit-

ting highly noise immune digital data back to the host proc-

essor

To understand the operation of these converters it is best to

refer to the Timing Diagram and Functional Block Diagram

and to follow a complete conversion sequence

1 A conversion is initiated by first pulling the CS (chip se-

lect) line low This line must be held low for the entire con-

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

MUX assignment word

2 A clock is then generated by the processor (if not provid-

ed continuously) and output to the AD clock input

3 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 con-

verter expects the next 4 bits to be the MUX assignment

word

4 Single-Ended

2 Differential

Mixed Mode

TLH5607 – 6

FIGURE 1 Analog Input Multiplexer Options for the ADC0833

ADC0833 Datasheet(PDF) 10 Page - National Semiconductor (TI)