Chapter 5 Resets, Interrupts, and General System Control
MC9S08QL8 MCU Series Reference Manual, Rev. 1
NXP Semiconductors
63
5.6
Low-Voltage Detect (LVD) System
The MC9S08QL8 series include a system to protect against low voltage conditions to protect memory
contents and control MCU system states during supply voltage variations. The system is comprised of a
power-on reset (POR) circuit and a LVD circuit. The LVD circuit is enabled when LVDE in SPMSC1 is
set. The LVD is disabled upon entering either of the stop modes unless LVDSE is set in SPMSC1. If
LVDSE and LVDE are both set, then the MCU will enter stop3 instead of stop2, and the current
consumption in stop3 with the LVD enabled will be greater.
5.6.1
Power-On Reset Operation
When power is initially applied to the MCU, or when the supply voltage drops below the power-on reset
rearm voltage level, V
POR
, the POR circuit will cause a reset condition. As the supply voltage rises, the
LVD circuit will hold the MCU in reset until the supply has risen above the low voltage detection low
threshold, V
LVDL
. Both the POR bit and the LVD bit in SRS are set following a POR.
5.6.2
Low-Voltage Detection (LVD) Reset Operation
The LVD can be configured to generate a reset upon detection of a low voltage condition by setting
LVDRE to 1. After an LVD reset has occurred, the LVD system will hold the MCU in reset until the supply
voltage has risen above the low voltage detection threshold. The LVD bit in the SRS register is set
following either an LVD reset or POR.
5.6.3
Low-Voltage Detection (LVD) Interrupt Operation
When a low voltage condition is detected and the LVD circuit is configured using SPMSC1 for interrupt
operation (LVDE set, LVDIE set, and LVDRE clear), then LVDF in SPMSC1 will be set and an LVD
interrupt request will occur. The LVDF bit is cleared by writing a 1 to the LVDACK bit in SPMSC1.
5.6.4
Low-Voltage Warning (LVW) Interrupt Operation
The LVD system has a low voltage warning flag (LVWF) to indicate to the user that the supply voltage is
approaching, but remains above, the LVD voltage. The LVW also has an interrupt associated with it,
enabled by setting the LVWIE bit in the SPMSC3 register. If enabled, an LVW interrupt request will occur
when the LVWF is set. LVWF is cleared by writing a 1 to the LVWACK bit in SPMSC3.
5.7
Peripheral Clock Gating
The MC9S08QL8 series include a clock gating system to manage the bus clock sources to the individual
peripherals. Using this system, the user can enable or disable the bus clock to each of the peripherals at the
clock source, eliminating unnecessary clocks to peripherals which are not in use and thereby reducing the
overall run and wait mode currents.
Out of reset, all peripheral clocks will be enabled. For lowest possible run or wait currents, user software
must disable the clock source to any peripheral not in use. The actual clock will be enabled or disabled
immediately following the write to the clock gating control registers (SCGC1 and SCGC2). Any
Содержание MC9S08QL4
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Страница 24: ...Chapter 2 Pins and Connections MC9S08QL8 MCU Series Reference Manual Rev 1 24 NXP Semiconductors...
Страница 36: ...Chapter 3 Modes of Operation MC9S08QL8 MCU Series Reference Manual Rev 1 36 NXP Semiconductors...
Страница 56: ...Chapter 4 Memory MC9S08QL8 MCU Series Reference Manual Rev 1 56 NXP Semiconductors...
Страница 120: ...Analog Comparator S08ACMPVLPV1 MC9S08QL8 MCU Series Reference Manual Rev 1 120 NXP Semiconductors...
Страница 148: ...Analog to Digital Converter S08ADC12V1 MC9S08QL8 MCU Series Reference Manual Rev 1 148 NXP Semiconductors...
Страница 162: ...Internal Clock Source S08ICSV3 MC9S08QL8 MCU Series Reference Manual Rev 0 162 NXP Semiconductors...
Страница 172: ...Modulo Timer S08MTIMV1 MC9S08QL8 MCU Series Reference Manual Rev 1 172 NXP Semiconductors...
Страница 200: ...Serial Communications Interface S08SCIV4 MC9S08QL8 MCU Series Reference Manual Rev 1 200 NXP Semiconductors...
Страница 224: ...Timer Pulse Width Modulator S08TPMV3 MC9S08QL8 MCU Series Reference Manual Rev 1 224 NXP Semiconductors...
Страница 238: ...Development Support MC9S08QL8 MCU Series Reference Manual Rev 1 238 NXP Semiconductors...
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