HT85F2240 datasheet(72/147 Pages) HOLTEK

72 / 147 page

Rev. 1.10

7� of 147

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A/D Flash 8051 Core Low Pin Count MCU

HT85F2230/HT85F2240

Watchdog Reset

All devices contain a Watchdog Timer which is used as a protection feature. The Watchdog

Timer has to be periodically cleared by the application program and prevented from overflowing

during normal MCU operation. However should the program enter an endless loop or should

external environmental conditions such as noise causes the device to jump to unpredicted program

locations, the Watchdog Timer will overflow and generate an MCU reset. Refer to the Watchdog

Timer section for more details regarding the Watchdog Timer operation.

When a Watchdog Reset occurs the WDTS bit in the IP0 register will be set to indicate the reset

source. Note that this bit must be reset by the application program.

IP0 Register

SFR Address: B8h

Bit

Name

—

WDTS

PT�

—

PT1

PX1

PT0

PX0

R/W

—

R/W

—

R/W

POR

—

Bit 7

Unimplemented, read as “0”

Bit 6

WDTS: Watchdog timer reset indication flag

0: No Watchdog timer reset

1: Watchdog timer reset

This bit must be cleared by the application program as it will not be automatically

cleared by hardware.

Bit 5

PT2: Timer 2 Interrupt priority

Described elsewhere

Bit 4

Unimplemented, read as “0”

Bit 3

PT1: Timer 1 Interrupt priority

Described elsewhere

Bit 2

PX1: External interrupt 1 priority

Described elsewhere

Bit 1

PT0: Timer 0 Interrupt priority

Described elsewhere

Bit 0

PX0: External interrupt 0 priority

Described elsewhere

Software Resets

There are three ways to generate Software Reset, each of which are generated by writing certain

values to the SRST register, the WDTCR register or the LVRCR register.

Software Reset Summary

Software Reset Name

Operation Objects

Operation

Bit

SRST Register setting

SRST

SRSTREQ

Write two s�ccessive “1” va��es to this bit

WDTCR Register setting

WDTCR

WE4~WE0

Write va��e other than “10101” or “01010”

LVRCR Register setting

LVRCR

LVS7~LVS0

Write va��e other than “01010101”� “00110011”�

“011001” or “10101010”

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