PIC18F2331/2431/4331/4431
The block diagram for the LVD module is shown in
Figure 22-1.
22.0 LOW-VOLTAGE DETECT (LVD)
PIC18F2331/2431/4331/4431 devices have a Low-
Voltage Detect module (LVD), a programmable circuit
that enables the user to specify a device voltage trip
point. If the device experiences an excursion below the
trip point, 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 module is enabled by setting the LVDEN bit, but
the circuitry requires some time to stabilize each time
that it is enabled. The IRVST bit is a read-only bit used
to indicate when the circuit is stable. The module can
only generate an interrupt after the circuit is stable and
the IRVST bit is set. The module monitors for drops in
VDD below a predetermined set point.
The Low-Voltage Detect Control register (Register 22-1)
completely controls the operation of the LVD module.
This allows the circuitry to be “turned off” by the user
under software control, which minimizes the current
consumption for the device.
REGISTER 22-1: LVDCON: LOW-VOLTAGE DETECT CONTROL REGISTER
U-0
—
U-0
—
R-0
R/W-0
R/W-0
LVDL3(1)
R/W-1
LVDL2(1)
R/W-0
LVDL1(1)
R/W-1
LVDL0(1)
IRVST
LVDEN
bit 7
bit 0
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
bit 7-6
bit 5
Unimplemented: Read as ‘0’
IRVST: Internal Reference Voltage Stable Flag bit
1= Indicates that the Low-Voltage Detect logic will generate the interrupt flag at the specified voltage
range
0= Indicates that the Low-Voltage Detect logic will not generate the interrupt flag at the specified
voltage range and the LVD interrupt should not be enabled
bit 4
LVDEN: Low-Voltage Detect Power Enable bit
1= Enables LVD, powers up LVD circuit
0= Disables LVD, powers down LVD circuit
bit 3-0
LVDL<3:0>: Low-Voltage Detection Limit bits(1)
1111= External analog input is used (input comes from the LVDIN pin)
1110= Maximum setting
.
.
.
0010= Minimum setting
0001= Reserved
0000= Reserved
Note 1: LVDL<3:0> bit modes, which result in a trip point below the valid operating voltage of the device, are not
tested.
2010 Microchip Technology Inc.
DS39616D-page 257
MICROCHIP [ MICROCHIP ]
