Z8F1601 Datasheet, PDF (45/246 Pages) Zilog, Inc. – Z8 Encore Microcontrollers with Flash Memory and 10-Bit A/D Converter

Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x
Z8 Encore!^®
27
Power-On Reset
The Z8F640x family products contain an internal Power-On Reset (POR) circuit. The
POR circuit monitors the supply voltage and holds the device in the Reset state until the
supply voltage reaches a safe operating level. After the supply voltage exceeds the POR
voltage threshold (V_POR), the POR Counter is enabled and counts 514 cycles of the
Watch-Dog Timer oscillator. After the POR counter times out, the XTAL Counter is
enabled to count a total of 16 system clock pulses. The Z8F640x family device is held in
the Reset state until both the POR Counter and XTAL counter have timed out. After the
device exits the Power-On Reset state, the eZ8 CPU fetches the Reset vector. Following
Power-On Reset, the POR status bit in the Watch-Dog Timer Control (WDTCTL) register
is set to 1.
Figure 62 illustrates Power-On Reset operation. Refer to the Electrical Characteristics
chapter for the POR threshold voltage (V_POR).
V_POR
V_VBO
VCC = 0.0V
VCC = 3.3V
Program
Execution
WDT Clock
Crystal Oscillator
XOUT
Internal RESET
signal
Oscillator
Start-up
POR
counter delay
XTAL
counter delay
Figure 62. Power-On Reset Operation (not to scale)
Voltage Brown-Out Reset
The devices in the Z8F640x family provide low Voltage Brown-Out (VBO) protection.
The VBO circuit senses when the supply voltage drops to an unsafe level (below the VBO
PS017610-0404
Reset and Stop Mode Recovery