Low-Voltage Inhibit (LVI)
Functional Description
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Low-Voltage Inhibit (LVI) 337
18.4.1 Polled LVI Operation
In applications that can operate at VDD levels below VLVRX, software can
monitor VDD by polling the LVIOUT bit. In the configuration register, the
LVIPWR bit must be at logic 1 to enable the LVI module, and the LVIRST
bit must be at logic 0 to disable LVI resets. See Section 5.
Configuration Register (CONFIG). TRPSEL in the LVISCR selects
VLVRX.
18.4.2 Forced Reset Operation
In applications that require VDD to remain above VLVRX, enabling LVI
resets allows the LVI module to reset the MCU when VDD falls to the
VLVRX level and remains at or below that level for nine or more
consecutive CPU cycles. In the CONFIG register, the LVIPWR and
LVIRST bits must be at logic 1 to enable the LVI module and to enable
LVI resets. TRPSEL in the LVISCR selects VLVRX.
18.4.3 False Reset Protection
The VDD pin level is digitally filtered to reduce false resets due to power
supply noise. In order for the LVI module to reset the MCU, VDD must
remain at or below VLVRX for nine or more consecutive CPU cycles. VDD
must be above VLVRX + VLVHX for only one CPU cycle to bring the MCU
out of reset. TRPSEL in the LVISCR selects VLVRX + VLVHX.
Addr. Register Name Bit 7654321Bit 0
$FE0F LVI Status and Control
Register (LVISCR)
See page 338.
Read: LVIOUT 0 TRPSEL 00000
Write:RR RRRRR
Reset:00000000
R= Reserved
Figure 18-2. LVI I/O Register Summary