LM3S2B93 Datasheet, PDF (934/1194 Pages) Texas Instruments – Stellaris® LM3S2B93 Microcontroller

Analog Comparators
In each range, the internal reference, V_IREF, has 16 pre-programmed thresholds or step values. The
threshold to be used to compare the external input voltage against is selected using the VREF field
in the ACREFCTL register.
In the high-range mode, the V_IREF threshold voltages start at the ideal high-range starting voltage
of V_DDA/3.875 and increase in ideal constant voltage steps of V_DDA/31.
In the low-range mode, the V_IREF threshold voltages start at:0V and increase in ideal constant voltage
steps of V_DDA/23. The ideal V_IREF step voltages for each mode and their dependence on the RNG
and VREF fields are summarized in Table 19-3 on page 934.
Table 19-3. Internal Reference Voltage and ACREFCTL Field Values
ACREFCTL Register
EN Bit
Value
RNG Bit Value ^{Output Reference Voltage Based on VREF Field Value}
EN=0
RNG=X
0 V (GND) for any value of VREF. It is recommended that RNG=1 and VREF=0 to minimize noise
on the reference ground.
RNG=0 Total resistance in ladder is 31 R.
VIREF = VDDA × ^RVREF
VIREF
V^VI^IR^RE^EF^F
=
=⁼
VDDA
V^VDDD^DA^A
×
×^×
RV^RR^TEF
R_(VV_RRR_TE_EF_F
RT
+ 8)
EN=1
RNG=1
TTohte^VVVV_VVVV^VV_VVVV^VV_VVVVV^VVV_alr^I_I^I_I^I_IIII^III_III^II_IIII^IIIar^RRR_RRRRRRRRR^RRRRR_RRRR^RRR_enEEE^EEE_EEEEEEs^EEEEE_EEEE^EEEgi^FFF_FFFFFFFFF^FFFFFFFF_FFFFsetaonf⁼⁼⁼⁼₌⁼⁼₌₌₌₌⁼⁼⁼_=======⁼⁼_=cinete^VV_VVVV^VVVV_VVVVVV^VVV000_000000inrn^DDD_D^D_D^D_D^D_D^D_DD^DD_DDDD^..._{......laaDDDDD}^DDDD_D^DD_DDDD^DDD888₈₈₈₁₁₁ld_AAAAA^AAAA_A^AAAAA_AAAArd₄₄₄⁵⁵⁵₅₅₅eef^{××××}_{××××××}^××_{××××}^×××e_333r r⁺⁺⁺_+++ise^V_VVVV^RRR_RRR^RRR((((_{(×××}n2^VVVV_Vc⁰⁰⁰₀₀₀^R_RRRR3^VVVVVV_VVV^R_R^RRRRR₂₂₂₂e^RRRR_RVVV^RRRRRR_RRR^..._...R^E_EEEE^TT_T^TTTTTT₃₃₃₃i^EEEEEE_EEE^EEEE_En_RRR.¹¹¹₁₁₁^F_FFFF^FFFFFF_FFF³³³³₃₃^FFFF_Ft_EEEh⁰⁰⁰₀₀₀¹¹¹¹₁₁i_FFFs⁶⁶⁶₆₆₆⁺⁺⁺⁺₊mo^×××_×××⁸⁸⁸⁸₈de^VVV_VVV⁾⁾⁾⁾₎is^RRR_RRR0^EEE_EEE.8^FFF_FFF5-2.448 V.
VIREF = V0D.D1A4×3 ^V×^R2V^E3R^FEF
VIREF = 0.143 ײV³REF
VIREF = 0.143 × VREF
19.4
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.
934
January 20, 2012
Texas Instruments-Production Data