LM3S5K36 Datasheet, PDF (535/1050 Pages) Texas Instruments – Stellaris® LM3S5K36 Microcontroller

Figure 12-9. External Voltage Conversion Result
0x3FF
0x2FF
0x1FF
0x0FF
Stellaris^® LM3S5K36 Microcontroller
0.00 V
½ V_REFA
V_REFA
V_DD
V_IN
- Input Saturation
12.3.5
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 12-3 on page 535). The ADC does not
support other differential pairings such as analog input 0 with analog input 3.
Table 12-3. 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:
■ If ∆V = 0, then the conversion result = 0x1FF
■ If ∆V > 0, then the conversion result > 0x1FF (range is 0x1FF–0x3FF)
■ If ∆V < 0, then the conversion result < 0x1FF (range is 0–0x1FF)
January 21, 2012
535
Texas Instruments-Production Data