MC9S08DZ60CLH Datasheet, PDF (75/416 Pages) Freescale Semiconductor, Inc – MC9S08DZ60 Series Features

Chapter 5 Resets, Interrupts, and General System Control
5.6 Low-Voltage Detect (LVD) System
The MC9S08DZ60 Series includes a system to protect against low-voltage conditions in order 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 with trip voltages for warning and
detection. The LVD circuit is enabled when LVDE in SPMSC1 is set to 1. The LVD is disabled upon
entering any of the stop modes unless LVDSE is set in SPMSC1. If LVDSE and LVDE are both set, then
the MCU cannot enter stop2 (it will enter stop3 instead), and the current consumption in stop3 with the
LVD enabled will be higher.
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. The low-voltage detection threshold is determined by the LVDV bit. 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 Warning (LVW) Interrupt Operation
The LVD system has a low-voltage warning flag to indicate to the user that the supply voltage is
approaching the low-voltage condition. When a low-voltage warning condition is detected and is
configured for interrupt operation (LVWIE set to 1), LVWF in SPMSC1 will be set and an LVW interrupt
request will occur.
5.7 MCLK Output
The PTA0 pin is shared with the MCLK clock output. If the MCSEL bits are all zeroes, the MCLK clock
is disabled. Setting any of the MCSEL bits causes the PTA0 pin to output a divided version of the internal
MCU bus clock regardless of the state of the port data direction control bit for the pin. The divide ratio is
determined by the MCSEL bits. The slew rate and drive strength for the pin are controlled by PTASE0 and
PTADS0, respectively. The maximum clock output frequency is limited if slew rate control is enabled, see
the electrical specifications for the maximum frequency under different conditions.
MC9S08DZ60 Series Data Sheet, Rev. 4
Freescale Semiconductor
75