ADC12030CIWM National Semiconductor, ADC12030CIWM Datasheet - Page 28

• 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
Status Bit
Status Bit
Function
Location
Tables
Application Hints
1.0 DIGITAL INTERFACE
1.1 Interface Concepts
The example in Figure 7 shows a typical sequence of events
after the power is applied to the ADC12030/2/4/8:
The first instruction input to the A/D via DI initiates Auto Cal.
The data output on DO at that time is meaningless and is
completely random. To determine whether the Auto Cal has
been completed, a read status instruction is issued to the
A/D. Again the data output at that time has no significance
since the Auto Cal procedure modifies the data in the output
shift register. To retrieve the status information, an additional
read status instruction is issued to the A/D. At this time the
status data is available on DO. If the Cal signal in the status
word, is low Auto Cal has been completed. Therefore, the
next instruction issued can start a conversion. The data out-
put at this time is again status information. To keep noise
from corrupting the A/D conversion, status can not be read
during a conversion. If CS is strobed and is brought low dur-
ing a conversion, that conversion is prematurely ended.
EOC can be used to determine the end of a conversion or
the A/D controller can keep track in software of when it would
be appropriate to comnmunicate to the A/D again. Once it
has been determined that the A/D has completed a conver-
sion, another instruction can be transmitted to the A/D. The
data from this conversion can be accessed when the next in-
struction is issued to the A/D.
Note, when CS is low continuously it is important to transmit
the exact number of SCLK cycles, as shown in the timing
diagrams. Not doing so will desynchronize the serial commu-
nication to the A/D. (See Section 1.3.)
FIGURE 7. Typical Power Supply Power Up Sequence
“High”
indicates
a Power
Up
Sequence
is in
progress
(Continued)
DB0
PU
Device Status
“High”
indicates
a Power
Down
Sequence
is in
progress
DB1
PD
“High”
indicates
an
Auto-Cal
Sequence
is in
progress
DB2
Cal
TABLE 7. Status Register
“High”
indicates
an 8 or 9
bit format
DS011354-36
8 or 9
DB3
28
“High”
indicates
a 12 or
13 bit
format
12 or 13
DB4
1.2 Changing Configuration
The configuration of the ADC12030/2/4/8 on power up de-
faults to 12-bit plus sign resolution, 12- or 13-bit MSB First,
10 CCLK acquisition time, user mode, no Auto Cal, no Auto
Zero, and power up mode. Changing the aquisition time and
turning the sign bit on and off requires an 8-bit instruction to
be issued to the ADC. This instruction will not start a conver-
sion. The instructions that select a multiplexer address and
format the output data do start a conversion. Figure 8 de-
scribes an example of changing the configuration of the
ADC12030/2/4/8.
During I/O sequence 1, the instruction on DI configures the
ADC12030/2/4/8 to do a conversion with 12-bit +sign resolu-
tion. Notice that when the 6 CCLK Acquisition and Data Out
without Sign instructions are issued to the ADC, I/O se-
quences 2 and 3, a new conversion is not started. The data
output during these instructions is from conversion N which
was started during I/O sequence 1. The Configuration Modi-
fication timing diagram describes in detail the sequence of
events necessary for a Data Out without Sign, Data Out with
Sign, or 6/10/18/34 CCLK Acquisition time mode selection.
Table 5 describes the actual data necessary to be input to
the ADC to accomplish this configuration modification. The
next instruction, shown in Figure 8 , issued to the A/D starts
conversion N+1 with 8 bits of resolution formatted MSB first.
Again the data output during this I/O cycle is the data from
conversion N.
The number of SCLKs applied to the A/D during any conver-
sion I/O sequence should vary in accord with the data out
word format chosen during the previous conversion I/O se-
quence. The various formats and resolutions available are
shown in Table 1 . In Figure 8 , since 8-bit without sign MSB
first format was chosen during I/O sequence 4, the number
of SCLKs required during I/O sequence 5 is 8. In the follow-
ing I/O sequence the format changes to 12-bit without sign
MSB first; therefore the number of SCLKs required during
I/O sequence 6 changes accordingly to 12.
DO Output Format Status
“High”
indicates
a 16 or
17 bit
format
16 or 17
DB5
“High”
indicates
that the
sign bit is
included.
When
“Low” the
sign bit is
not
included.
Sign
DB6
Justification
When
“High” the
conversion
result will
be output
MSB first.
When
“Low” the
result will
be output
LSB first.
DB7
When
“High” the
device is in
test mode.
When
“Low” the
device is in
user mode.
Test Mode
DB8