Z8F2402 datasheet(45/246 Pages) ZILOG

45 / 246 page

PS017610-0404

Reset and Stop Mode Recovery

Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x

Z8 Encore!®

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 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 (VPOR).

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

VCC = 0.0V

VCC = 3.3V

VPOR

VVBO

Crystal Oscillator

XOUT

Internal RESET

signal

Program

Execution

Oscillator

Start-up

XTAL

WDT Clock

POR

counter delay

Z8F2402 Datasheet(PDF) 45 Page - Zilog, Inc.