Z8F082ASH020SC datasheet(98/244 Pages) ZILOG

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PS024705-0405

P R E L I M I N A R Y

Watch-Dog Timer

Z8 Encore! XP® F08xA Series

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 counts down to 000000H unless a WDT

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

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

Reload registers. Counting resumes following the reload operation.

When the Z8 Encore! XP® F08xA Series devices are operating in DEBUG Mode (using

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

Watch-Dog Timer time-outs.

Watch-Dog Timer Time-Out Response

The Watch-Dog Timer times out when the counter reaches 000000H. A time-out of the

Watch-Dog Timer generates either an interrupt or a system reset. The WDT_RES Flash

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

“Flash Option Bits” on page 138

for information regarding programming of the WDT_RES

Flash Option Bit.

WDT Interrupt in Normal Operation

If configured to generate an interrupt when a time-out occurs, the Watch-Dog Timer issues

an interrupt request to the interrupt controller and sets the WDT status bit in the Watch-Dog

Timer Control register. If interrupts are enabled, the eZ8 CPU responds to the interrupt

request by fetching the Watch-Dog Timer interrupt vector and executing code from the

vector address. After time-out and interrupt generation, the Watch-Dog Timer counter

rolls over to its maximum value of FFFFFH and continues counting. The Watch-Dog

Timer counter is not automatically returned to its Reload Value.

The Reset Status Register (page 26) must be read before clearing the WDT interrupt. This

read clears the WDT timeout flag and prevents further WDT interrupts for immediately

occurring.

Table 55. 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

000004

400

µs

Minimum time-out delay

FFFFFF

16,777,215

28 minutes

Maximum time-out delay

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