MC68HC908GT16_07 Datasheet, PDF (114/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

Low-Voltage Inhibit (LVI)
LVISTOP, LVIPWRD, LVI5OR3, and LVIRSTD are in the configuration register (CONFIG1). See Figure
4-2. Configuration Register 1 (CONFIG1) for details of the LVI’s configuration bits. Once an LVI reset
occurs, the MCU remains in reset until V_DD rises above a voltage, V_TRIPR, which causes the MCU to exit
reset. See 15.3.2.5 Low-Voltage Inhibit (LVI) Reset for details of the interaction between the SIM and the
LVI. The output of the comparator controls the state of the LVIOUT flag in the LVI status register (LVISR).
An LVI reset also drives the RST pin low to provide low-voltage protection to external peripheral devices.
V_DD
LVIPWRD
FROM CONFIG
STOP INSTRUCTION
FROM CONFIG1
LVIRSTD
LVISTOP
FROM CONFIG1
LOW V_DD
DETECTOR
V_DD > LVI_Trip = 0
V_DD ≤ LVI_Trip = 1
LVI5OR3
FROM CONFIG1
LVIOUT
Figure 10-1. LVI Module Block Diagram
LVI RESET
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
LVI Status Register ^{Read: LVIOUT}
0
0
0
0
0
0
0
$FE0C
(LVISR) Write:
See page 115. _Reset:
0
0
0
0
0
0
0
0
= Unimplemented
Figure 10-2. LVI I/O Register Summary
10.3.1 Polled LVI Operation
In applications that can operate at V_DD levels below the V_TRIPF level, software can monitor V_DD by polling
the LVIOUT bit. In the configuration register, the LVIPWRD bit must be at 0 to enable the LVI module, and
the LVIRSTD bit must be at 1 to disable LVI resets.
10.3.2 Forced Reset Operation
In applications that require V_DD to remain above the V_TRIPF level, enabling LVI resets allows the LVI
module to reset the MCU when V_DD falls below the V_TRIPF level. In the configuration register, the
LVIPWRD and LVIRSTD bits must be at 0 to enable the LVI module and to enable LVI resets.
10.3.3 Voltage Hysteresis Protection
Once the LVI has triggered (by having V_DD fall below V_TRIPF), the LVI will maintain a reset condition until
V_DD rises above the rising trip point voltage, V_TRIPR. This prevents a condition in which the MCU is
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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