Application hints – Rainbow Electronics ADC12038 User Manual
Page 29
Application Hints
(Continued)
1 6 User Mode and Test Mode
An instruction may be issued to the ADC to put it into test
mode Test mode is used by the manufacturer to verify com-
plete functionality of the device During test mode CH0 –
CH7 become active outputs If the device is inadvertently
put into the test mode with CS continuously low the serial
communications may be desynchronized Synchronization
may be regained by cycling the power supply voltage to the
device Cycling the power supply voltage will also set the
device into user mode If CS is used in the serial interface
the ADC may be queried to see what mode it is in This is
done by issuing a ‘‘read STATUS register’’ instruction to the
ADC When bit 9 of the status register is high the ADC is in
test mode when bit 9 is low the ADC is in user mode As an
alternative to cycling the power supply an instruction se-
quence may be used to return the device to user mode This
instruction sequence must be issued to the ADC using CS
The following table lists the instructions required to return
the device to user mode
Instruction
DI Data
DI0 DI1 DI2 DI3 DI4 DI5 DI6 DI7
TEST MODE
H
X
X
X
H
H
H
H
Instructions
Test Mode
Reset
L
L
L
L
H
H
H
L
L
L
L
L
H
L
H
L
L
L
L
L
H
L
H
H
USER MODE
L
L
L
L
H
H
H
H
Power Up
L
L
L
L
H
L
H
L
Set DO with
H
or without
or
L
L
L
H
H
L
H
Sign
L
Set
H
H
Acquisition
or
or
L
L
H
H
H
L
Time
L
L
Start
H
H
H
H
H
H
H
a
or
or
or
or
L
or
or
or
Conversion
L
L
L
L
L
L
L
X
e
Don’t Care
After returning to user mode with the user mode instruction
the power up data with or without sign and acquisition time
instructions need to be resent to ensure that the ADC is in
the required state before a conversion is started
1 7 Reading the Data Without Starting a Conversion
The data from a particular conversion may be accessed
without starting a new conversion by ensuring that the
CONV line is taken high during the I O sequence See the
Read Data timing diagrams Table VI describes the opera-
tion of the CONV pin
2 0 DESCRIPTION OF THE ANALOG MULTIPLEXER
For the ADC12038 the analog input multiplexer can be con-
figured with 4 differential channels or 8 single ended chan-
nels with the COM input as the zero reference or any combi-
nation thereof (see
Figure 7
) The difference between the
voltages on the V
REF
a
and V
REF
b
pins determines the
input voltage span (V
REF
) The analog input voltage range is
0 to V
A
a
Negative digital output codes result when V
IN
b
l
V
IN
a
The actual voltage at V
IN
b
or V
IN
a
cannot go below
AGND
4 Differential
Channels
TL H 11354 – 38
FIGURE 7
CH0 CH2 CH4 and CH6 can be assigned to the MUX-
OUT1 pin in the differential configuration while CH1 CH3
CH5 and CH7 can be assigned to the MUXOUT2 pin In the
differential configuration the analog inputs are paired as fol-
lows CH0 with CH1 CH2 with CH3 CH4 with CH5 and CH6
with CH7 The A DIN1 and A DIN2 pins can be assigned
positive or negative polarity
8 Single-Ended Channels
with COM
as Zero Reference
TL H 11354 – 39
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