Z8F6421PM020SC Datasheet, PDF (65/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
45
voltage threshold (V_POR), the POR Counter is enabled and counts 66 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 devices are held in the Reset state until both
the POR Counter and XTAL counter have timed out. After the 64K Series devices exit 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 8 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
Primary
Oscillator
Internal RESET
signal
Oscillator
Start-up
Not to Scale
POR
counter delay
Figure 8. Power-On Reset Operation)
XTAL
counter delay
Voltage Brown-Out Reset
The devices in the 64K Series provide low Voltage Brown-Out (VBO) protection. The
VBO circuit senses when the supply voltage drops to an unsafe level (below the VBO
threshold voltage) and forces the device into the Reset state. While the supply voltage
remains below the Power-On Reset voltage threshold (V_POR), the VBO block holds the
device in the Reset state.
After the supply voltage again exceeds the Power-On Reset voltage threshold, the devices
progress through a full System Reset sequence, as described in the Power-On Reset sec-
PS019915-1005
Reset and STOP Mode Recovery