UM10346_1
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 01 — 2 November 2009
93 of 132
NXP Semiconductors
UM10346
LPC980/982 User manual
13.2 Selectable internal reference voltage
An internal reference voltage generator may be used to supply a default reference when a
single comparator input pin is used. The user may program one of eight different values
for the internal reference voltage using the Comparator Reference register (CMPREF).
Each of the two comparators may use a different reference voltage. Please refer to the
P89LPC980/982
data sheet
for specifications.
(1) See
for more details..
Fig 44. Comparator input and output connections
comparator 1
CP1
CN1
(P0.4) CIN1A
(P0.3) CIN1B
(P0.5) CMPREF
V
ref(cmp)
(1)
OE1
change detect
CO1
CMF1
interrupt
002aac346
CMP1 (P0.6)
EC
change detect
CMF2
comparator 2
OE2
CO2
CMP2 (P0.0)
CP2
CN2
(P0.2) CIN2A
(P0.1) CIN2B
Table 78.
Comparator Reference register (CMPREF - address FFCBh) bit allocation
Bit
7
6
5
4
3
2
1
0
Symbol
-
REFS5
REFS4
REFS3
-
REFS2
REFS1
REFS0
Reset
x
0
0
0
x
0
0
0
Table 79.
Comparator Reference register (CMPREF - address FFCBh) bit description
Bit Symbol
Description
2:0
REFS2:0 Reference Select for Comparator 1. These bits are used to select the internal
reference voltage for Comparator 1.
The following references for Comparator 1 are selected by reference bits
REFS[2:0]:
000 Bandgap voltage,Vref(bg) , nominally 1.23 V
001 Vref_trip1, 0.875 V
DD
.
010 Vref_trip2, 0.750 V
DD
.
011 Vref_trip3, 0.625 V
DD
.
100 Vref_trip4, 0.500 V
DD
.
101 Vref_trip5, 0.375 V
DD
.
110 Vref_trip6, 0.250 V
DD
.
111 Vref_trip7, 0.125 V
DD
.
3
-
Reserved