Datasheet

 2011 Microchip Technology Inc. DS39932D-page 373
PIC18F46J11 FAMILY
24.0 HIGH/LOW VOLTAGE DETECT
(HLVD)
PIC18F46J11 family devices (including PIC18LF46J11
family devices) have a High/Low Voltage Detect
(HLVD) module for monitoring the absolute voltage on
V
DD or the HLVDIN pin. This is a programmable circuit
that allows the user to specify both a device voltage trip
point and the direction of change from that point.
If the module detects an excursion past the trip point in
that direction, an interrupt flag is set. If the interrupt is
enabled, the program execution will branch to the inter-
rupt vector address and the software can then respond
to the interrupt.
The High/Low-Voltage Detect Control register
(Register 24-1) completely controls the operation of the
HLVD module. This allows the circuitry to be “turned
off” by the user under software control, which
minimizes the current consumption for the device.
Figure 24-1 provides a block diagram for the HLVD
module.
The module is enabled by setting the HLVDEN bit.
Each time the module is enabled, the circuitry requires
some time to stabilize. The IRVST bit is a read-only bit
that indicates when the circuit is stable. The module
can generate an interrupt only after the circuit is stable
and IRVST is set.
The VDIRMAG bit determines the overall operation of
the module. When VDIRMAG is cleared, the module
monitors for drops in V
DD below a predetermined set
point. When the bit is set, the module monitors for rises
in V
DD above the set point.
REGISTER 24-1: HLVDCON: HIGH/LOW-VOLTAGE DETECT CONTROL REGISTER (ACCESS F85h)
R/W-0 R-0 R-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
VDIRMAG BGVST IRVST HLVDEN HLVDL3
(1)
HLVDL2
(1)
HLVDL1
(1)
HLVDL0
(1)
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 VDIRMAG: Voltage Direction Magnitude Select bit
1 = Event occurs when voltage equals or exceeds trip point (HLVDL<3:0>)
0 = Event occurs when voltage equals or falls below trip point (HLVDL<3:0>)
bit 6 BGVST: Band Gap Reference Voltages Stable Status Flag bit
1 = Indicates internal band gap voltage references is stable
0 = Indicates internal band gap voltage reference is not stable
bit 5 IRVST: Internal Reference Voltage Stable Flag bit
1 = Indicates that the voltage detect logic will generate the interrupt flag at the specified voltage range
0 = Indicates that the voltage detect logic will not generate the interrupt flag at the specified voltage
range and the HLVD interrupt should not be enabled
bit 4 HLVDEN: High/Low-Voltage Detect Power Enable bit
1 = HLVD enabled
0 = HLVD disabled
bit 3-0 HLVDL<3:0>: Voltage Detection Limit bits
(1)
1111 = External analog input is used (input comes from the HLVDIN pin)
1110 = Maximum setting
.
.
.
1000 = Minimum setting
0xxx = Reserved
Note 1: See Table 29-8 in Section 29.0 “Electrical Characteristics” for specifications.