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 (VPOR), 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 PORstatus 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 (VPOR).
VCC = 3.3V
VPOR
VVBO
Program
Execution
VCC = 0.0V
WDT Clock
Crystal Oscillator
XOUT
Oscillator
Start-up
Internal RESET
signal
POR
XTAL
counter delay
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
ZILOG [ ZILOG, INC. ]
