n 2
sample
S
I
I
pext
S
t
(R
R ) ln(2
) (C
C
), R
< 10 kΩ
+
³
+
´
´
+
ADC12_B Operation
876
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
ADC12_B
The resistance of the source R
S
and R
I
affect t
Sample
. Use
to calculate the minimum sampling
time t
Sample
for a n-bit conversion, where n equals the bits of resolution.
(17)
See the device-specific data sheet for R
I
and C
I
values.
34.2.7 Conversion Memory
32 ADC12MEMx conversion memory registers store the conversion results. Each ADC12MEMx is
configured with an associated ADC12MCTLx control register. The ADC12VRSEL bits define the voltage
reference, and the ADC12INCHx and ADC12DIF bits select the input channels. The ADC12EOS bit
defines the end of sequence when a sequential conversion mode is used. A sequence rolls over from
ADC12MEM31 to ADC12MEM0 when the ADC12EOS bit in ADC12MCTL31 is not set.
The CSTARTADDx bits define the first ADC12MCTLx used for any conversion. If the conversion mode is
single-channel or repeat-single-channel, the CSTARTADDx points to the single ADC12MCTLx to be used.
If the conversion mode selected is either sequence-of-channels or repeat-sequence-of-channels,
CSTARTADDx points to the first ADC12MCTLx location to be used in a sequence. A pointer, not visible to
software, is incremented automatically to the next ADC12MCTLx in sequence when each conversion
completes. The sequence continues until an ADC12EOS bit in ADC12MCTLx is processed; this is, the last
control byte processed.
When conversion results are written to a selected ADC12MEMx, the corresponding flag in the
ADC12IFGRx register is set.
There are two formats available to read the conversion result from ADC12MEMx. When ADC12DF = 0,
the conversion is right justified and unsigned. For ADC12DF = 0 with ADC12DIF = 0 and 8-bit, 10-bit, and
12-bit resolutions, the upper 8, 6, and 4 bits, respectively, of an ADC12MEMx read are always zeros. To
convert a ADC12DIF = 1 to binary unsigned, the maximum negative value is added to the conversion.
Therefore, 128 is added for 8-bit conversions, 512 is added for 10-bit conversions, and 2048 is added for
12-bit conversions.
When ADC12DF = 1, the conversion result is left justified and two's complement. For 8-bit, 10-bit, and 12-
bit resolutions, the lower 8, 6, and 4 bits, respectively, of a ADC12MEMx read are always zeros.
summarizes the output data formats.
Table 34-1. ADC12_B Conversion Result Formats
Analog Input
Voltage Range
ADC12DIF
ADC12DF
ADC12RES
Ideal Conversion Results
(With Offset Added When
ADC12DIF = 1)
ADC12MEMx Read Value
Vin to V
R-
:
V
R-
to +V
R+
0
0
00
0 to 255
0000h to 00FFh
0
0
01
0 to 1023
0000h to 03FFh
0
0
10
0 to 4095
0000h to 0FFFh
0
1
00
-128 to 127
8000h to 7F00h
0
1
01
-512 to 511
8000h to 7FC0h
0
1
10
-2048 to 2047
8000h to 7FF0h
Vin+ to Vin-:
V
R-
to +V
R+
1
0
00
-128 to 127
(0 to 255)
0000h to 00FFh
1
0
01
-512 to 511
(0 to 1023)
0000h to 03FFh
1
0
10
-2048 to 2047
(0 to 4095)
0000h to 0FFFh
1
1
00
-128 to 127
8000h to 7F00h
1
1
01
-512 to 511
8000h to 7FC0h
1
1
10
-2048 to 2047
8000h to 7FF0h