Rainbow Electronics ADC0838 - Manual (Page 13)

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 50 mV above V
CC (typically 5V)
without 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 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 Diagrams and Functional Block Diagram
and to follow a complete conversion sequence For clarity a
separate diagram is shown of each device
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 A D 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 2 to 4 bits to be the MUX assign-
ment word
8 Single-Ended
4 Differential
8 Pseudo-Differential
Mixed Mode
TL H 5583 – 9
FIGURE 1 Analog Input Multiplexer Options for the ADC0838
13