ADC12030CIWM National Semiconductor, ADC12030CIWM Datasheet - Page 30

• Manufacturer Part Number: ADC12030CIWM
• Description: Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
• Manufacturer: National Semiconductor

www.national.com
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 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 communi-
cations may be desynchronized. Synchronization may be re-
gained 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 cy-
cling the power supply, an instruction sequence 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:
X = 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.
Set DO with
Instruction
Instructions
Conversion
Test Mode
Acquisition
Power Up
or without
MODE
MODE
USER
TEST
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
X
H
H
L
L
L
L
L
L
L
L
or
X
H
L
L
L
L
L
L
L
L
(Continued)
DI Data
or
X
H
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
or
H
H
H
H
H
L
L
L
L
L
30
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 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 9 ). The difference between the
voltages on the V
voltage span (V
V
The actual voltage at V
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.
With the single-ended multiplexer configuration CH0 through
CH7 can be assigned to the MUXOUT1 pin. The COM pin is
always assigned to the MUXOUT2 pin. A/DIN1 is assigned
as the positve input; A/DIN2 is assigned as the negative in-
put. (See Figure 10 ).
A
+
. Negative digital output codes result when V
REF
8 Single-Ended Channels
REF
). The analog input voltage range is 0 to
as Zero Reference
+
and V
4 Differential
IN
FIGURE 9.
with COM
Channels
−
or V
DS011354-39
REF
DS011354-38
IN
−
+
pins determines the input
cannot go below AGND.
IN
−
>
V
IN
+
.