adc12032 National Semiconductor Corporation, adc12032 Datasheet - Page 29

• Manufacturer Part Number: adc12032
• Description: Self-calibrating 12-bit Plus Sign Serial I/o A/d Converters With Mux And Sample/hold
• Manufacturer: National Semiconductor Corporation

Application Hints
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
complete functionality of the device. During test mode
CH0–CH7 become active outputs. If the device is inadvert-
ently put into the test mode with CS continuously low, the
serial communications may be desynchronized. Synchroni-
zation 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 inter-
face, 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:
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.
X = Don’t Care
USER MODE
TEST MODE
Set DO with
Instruction
Instructions
Conversion
Acquisition
Test Mode
Power Up
or without
Reset
Time
Start
Sign
Set
a
DI0 DI1 DI2 DI3 DI4 DI5 DI6 DI7
or
or
or
H
H
H
H
L
L
L
L
L
L
L
L
or
or
H
H
X
L
L
L
L
L
L
L
L
or
H
X
L
L
L
L
L
L
L
L
(Continued)
FIGURE 8. Changing the ADC’s Conversion Configuration
DI Data
or
H
X
L
L
L
L
L
L
L
L
H
H
H
H
H
H
H
H
L
or
H
H
H
H
H
H
L
L
L
L
or
H
H
H
H
H
H
H
H
L
L
01135437
or
H
H
H
H
H
L
L
L
L
L
29
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 6 describes the operation
of the CONV pin.
2.0 DESCRIPTION OF THE ANALOG MULTIPLEXER
For the ADC12038, the analog input multiplexer can be
configured with 4 differential channels or 8 single ended
channels with the COM input as the zero reference or any
combination thereof (see Figure 9). The difference between
the voltages on the V
input voltage span (V
0 to V
V
AGND.
IN
+
. The actual voltage at V
A
+
. Negative digital output codes result when V
8 Single-Ended Channels
as Zero Reference
REF
REF
4 Differential
FIGURE 9.
). The analog input voltage range is
with COM
Channels
+
and V
IN
01135439
−
01135438
REF
or V
−
IN
pins determines the
+
cannot go below
www.national.com
IN
−
>