LM3S1621 Datasheet, PDF (605/947 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex is a trademark

Stellaris^® LM3S1621 Microcontroller
Figure 13-6 on page 605 shows the ADC conversion function of the analog inputs when using an
external voltage reference.
The external voltage reference can be more accurate than the internal reference by using a
high-precision source or trimming the source.
Figure 13-6. External Voltage Conversion Result
0x3FF
0x2FF
0x1FF
0x0FF
0.00 V
½ V_REFA
V_REFA
V_DD
V_IN
- Input Saturation
13.3.5
Differential Sampling
In addition to traditional single-ended sampling, the ADC module supports differential sampling of
two analog input channels. To enable differential sampling, software must set the Dn bit in the
ADCSSCTL0n register in a step's configuration nibble.
When a sequence step is configured for differential sampling, the input pair to sample must be
configured in the ADCSSMUXn register. Differential pair 0 samples analog inputs 0 and 1; differential
pair 1 samples analog inputs 2 and 3; and so on (see Table 13-4 on page 605). The ADC does not
support other differential pairings such as analog input 0 with analog input 3.
Table 13-4. Differential Sampling Pairs
Differential Pair
0
1
2
3
Analog Inputs
0 and 1
2 and 3
4 and 5
6 and 7
The voltage sampled in differential mode is the difference between the odd and even channels:
∆V (differential voltage) = V_{IN_EVEN} (even channel) – V_{IN_ODD} (odd channel), therefore:
January 21, 2012
605
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