Low-Voltage Inhibit (LVI)
LVI Status Register
MC68HLC908QY/QT Family — Rev. 2
Data Sheet
MOTOROLA
Low-Voltage Inhibit (LVI)
91
10.3.4 LVI Trip Selection
The LVDLVR bit in the configuration register selects whether the LVI is configured
for LVD (low voltage detect) or LVR (low voltage reset) protection. The LVD trip
voltage can be used as a low voltage warning. The LVR trip voltage will commonly
be configured as a reset condition since it is very close to the minimum operating
voltage of the device. The LVDLVR bit can be written to anytime so that battery
applications can make use of the LVI as both a warning indicator and to generate
a system reset.
Polling and forced reset operation modes can be combined to take full advantage
of LVD and LVR trip voltages selection. LVD (LVDLVR = 1) in polling mode
(LVIRSTD = 1) can be used as a low voltage warning in a slowly and continuously
falling VDD application (for example, battery applications). Once LVD has been
identified, the part can be set to LVR (LVDLVR = 0) and reset enabled
(LVIRSTD = 0). So, as VDD continues to fall the part will reset when LVR trip
voltage is reached. Unlike other bits in CONFIG registers, LVIRSTD and LVDLVR
bits are allowed to be written multiple times after reset.
NOTE:
The microcontroller is guaranteed to operate at a minimum supply voltage. The trip
point (VTRIPF [LVD] or VTRIPF [LVR]) may be lower than this. See 16.5 DC 10.4 LVI Status Register
The LVI status register (LVISR) indicates if the VDD voltage was detected below
the VTRIPF level while LVI resets have been disabled.
LVIOUT — LVI Output Bit
This read-only flag becomes set when the VDD voltage falls below the VTRIPF
trip voltage and is cleared when VDD voltage rises above VTRIPR. The difference
in these threshold levels results in a hysteresis that prevents oscillation into and
out of reset (see Table 10-1). Reset clears the LVIOUT bit.
Address: $FE0C
Bit 7
6
54
32
1
Bit 0
Read:
LVIOUT
0
00
0
R
Write:
Reset:
000
00
0
= Unimplemented
R
= Reserved
Figure 10-2. LVI Status Register (LVISR)
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