LM3S9B81 Datasheet, PDF (1006/1155 Pages) Texas Instruments – Stellaris® LM3S9B81 Microcontroller

Analog Comparators
Table 21-3. Internal Reference Voltage and ACREFCTL Field Values
ACREFCTL Register
Output Reference Voltage Based on VREF Field Value
EN Bit
Value
RNG Bit Value
EN=0
RNG=X
0 V (GND) for any value of VREF; however, it is recommended that RNG=1 and VREF=0 for the
least noisy ground reference.
EN=1
RNG=0 Total resistance in ladder is 31 R.
RNG=1
VIREF = VDDA × ^RVREF
TTohte^VVVVV_VVVV^VVV_VVV^VV_VV^V_VV^VVVVValr^I_I^I_I^I_IIII^IIIII_II^III_III^IIIIIarRRR_RRRRRR^R_RR^RRRRRRR_RRR^RRRRRen_EEE^EEE_EEE^E_EEs^EEEEEEE_EEE^EEEEEgiFFF_FFFFFF^F_FF^FFFFFFFFFFFF_FFFsetaonf⁼⁼⁼⁼⁼₌⁼⁼⁼₌₌₌⁼⁼⁼⁼⁼₌₌₌⁼₌₌₌⁼⁼₌cinete^VVV_VVV^VVVVV_V^V_VVVV^VVVVV000₀₀₀₀₀₀inrn^DDDDDDDD_D^D_D^D_D^D_DD^DDD_DDD^..._......laa^D_DDDD^DDDDD_D^DDD_DDD^DDDDD888₈₈₈₁₁₁^ldA_AAAA^AAAAA_A^AAAAAAAA_AAA^rd₄₄₄⁵⁵⁵₅₅₅^{eef×××××}_×^×_{××××}^×××_×××^{×××××e}₃₃₃r ^r+++₊₊₊ise^V_VVVV^RRR_RRR^RRRRR((((((_×××^n2VVVVVVc000₀₀₀^R_RRRR3^VVVVVVVV_VVV^RRRRRRRRRR₂₂₂₂^eRRRRRR_VVV^RRRRRRRR_RRR^..._...R^E_EEEE^TTTTTTTTTTTT₃₃₃₃^iEEEEEEEE_EEE^EEEEEEn_RRR.¹¹¹₁₁₁^F_FFFF^FFFFFFFF_FFF³³³³³₃^FFFFFFt_EEE^h000₀₀₀¹¹¹¹¹₁ⁱ_FFF^s666₆₆₆^{++++++mo×××}_×××^888888deVVV_VVV^))))))isRRR_RRR^0EEE_EEE^.8FFF_FFF^{5-2.448 V.}
VIREF = V0D.D1A4×3 ^V×^R2V^E3R^FEF
VIREF = 0.143 ײV³REF
VIREF = 0.143 × VREF
21.4
The range of internal reference for this mode is 0-2.152 V.
Initialization and Configuration
The following example shows how to configure an analog comparator to read back its output value
from an internal register.
1. Enable the analog comparator 0 clock by writing a value of 0x0010.0000 to the RCGC1 register
in the System Control module (see page 174).
2. In the GPIO module, enable the GPIO port/pin associated with the input signals as GPIO inputs.
To determine which GPIO to configure, see Table 23-4 on page 1036.
3. Configure the PMCn fields in the GPIOPCTL register to assign the analog comparator output
signals to the appropriate pins (see page 336 and Table 23-5 on page 1043).
1006
Texas Instruments-Advance Information
June 29, 2010