ADC12L030CIWM National Semiconductor, ADC12L030CIWM Datasheet - Page 26

• Manufacturer Part Number: ADC12L030CIWM
• Description: 3.3V 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
in the power-down state. If a software power down instruc-
tion is issued to the ADC while a hardware power up is in ef-
fect (PD pin low), the device will power down. When the de-
vice is powered down by software, it may be powered up by
either issuing a software power up instruction or by taking
PD pin high and then low. If the power down command is is-
sued during an A/D conversion, that conversion is disrupted.
Therefore, the data output after power up cannot be relied
on.
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 low continuously, 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:
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
INSTRUCTIONS
USER MODE
TEST MODE
TEST MODE
Set DO with
Instruction
Conversion
Acquisition
Power Up
or without
RESET
Time
Sign
Start
Set
a
DI0
or
or
or
H
H
H
H
L
L
L
L
L
L
L
L
DI1
or
or
X
H
H
L
L
L
L
L
L
L
L
DI2
(Continued)
or
X
H
L
L
L
L
L
L
L
L
DI3
or
DI Data
H
X
L
L
L
L
L
L
L
L
DI4
H
H
H
H
H
H
H
H
L
DI5
or
H
H
H
H
H
H
L
L
L
L
DI6
or
H
H
H
H
H
H
H
H
L
L
DI7
or
H
H
H
H
H
L
L
L
L
L
26
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 ADC12L038, 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
put voltage span (V
to V
V
AGND.
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 positive input; A/DIN2 is assigned as the negative in-
put. (See Figure 10 ).
The Multiplexer assignment tables for the ADC12L030,2,4,8
( Tables 2, 3, 4 ) summarize the aforementioned functions for
the different versions of A/Ds.
IN
+
. The actual voltage at V
A
+
. Negative digital output codes result when V
8 Single-Ended Channels
REF
as Zero Reference
REF
). The analog input voltage range is 0
4 Differential
FIGURE 9.
+
with COM
Channels
and V
DS011830-39
DS011830-38
IN
REF
−
or V
−
pins determines the in-
IN
+
cannot go below
IN
−
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