ZUSBOPTSC01ZAC datasheet(86/402 Pages) ZILOG

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Watch-Dog Timer

P R E L I M I N A R Y

PS024604-1005

Z8 Encore!® Motor Control Flash MCUs

Product Specification

Watch-Dog Timer Refresh

When first enabled, the Watch-Dog Timer is loaded with the value in the Watch-Dog

Timer Reload registers. The Watch-Dog Timer then counts down to 0000h unless a WDT

instruction is executed by the eZ8 CPU. Execution of the WDT instruction causes the down-

counter to be reloaded with the WDT Reload value stored in the Watch-Dog Timer Reload

registers. Counting resumes following the reload operation.

When the Z8FMC16100 Series Flash MCU is operating in DEBUG Mode (through the

On-Chip Debugger), the Watch-Dog Timer is continuously refreshed to prevent spurious

Watch-Dog Timer time-outs.

Watch-Dog Timer Time-Out Response

The Watch-Dog Timer times out when the counter reaches 0000h. A time-out of the

Watch-Dog Timer generates either a system exception or a Reset. The WDT_RES Option

Bit determines the time-out response of the Watch-Dog Timer. Refer to the Option Bits

chapter for information regarding programming of the WDT_RES Option Bit.

WDT System Exception in Normal Operation

If configured to generate a system exception when a time-out occurs, the Watch-Dog

Timer issues an exception request to the interrupt controller. The eZ8 CPU responds to the

request by fetching the System Exception vector and executing code from the vector

address. After time-out and system exception generation, the Watch-Dog Timer is

reloaded automatically and continues counting.

WDT System Exception in Stop Mode

If configured to generate a system exception when a time-out occurs and the

Z8FMC16100 Series Flash MCU is in STOP mode, the Watch-Dog Timer automatically

initiates a Stop-Mode Recovery and generates a system exception request. Both the WDT

status bit and the STOP bit in the Reset Status and Control Register section on page 29 are

set to 1 following WDT time-out in STOP mode. Refer to the Reset and Stop-Mode

Recovery chapter on page 23 for more information.

Table 39. Watch-Dog Timer Approximate Time-Out Delays

WDT Reload

Value (Hex)

WDT Reload

Value

(Decimal)

Approximate Time-Out Delay

(with 10KHz Typical WDT Oscillator Frequency)

Typical

Description

0400

1024

102ms

Reset default value time-out delay.

FFFF

65,536

6.55s

Maximum time-out delay.

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