Rainbow Electronics ADC08138 - Manual (Page 14)

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 V
CC (typically 5V) with-
out degrading conversion accuracy
2 0 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
TL H 10749 – 16
FIGURE 1 Analog Input Multiplexer Options for the ADC08138
14