TTP258 datasheet(13/44 Pages) TONTEK

13 / 44 page

Preliminary

TTP258

TonTouch

16’/04/06

Page 13 of 44

Ver.: 1.2

S-6: Watch Dog Timer (WDT)

The clock of watchdog timer comes from time base overflow (TB1OV). User

can use the time up signal to prevent a software malfunction or abnormal

sequence from jumping to an unknown memory location causing a system fatal

failure. Normally, if the watchdog timer time up signal active that will reset the

chip. At the same time, program and hardware can be initialized and resume

system under normal operation. The chip also provides 2 steps clear watchdog

command as the programmer writes INTF with $F data first that will enable the

WDT clear, and then writes clear WDT 2nd register ($303H) after. Completely

finishes the two write & read steps will clear the watchdog timer. User should

well arrange the two command steps for avoiding the dead lock loop.

User should keep in minds that always reset WDT at main

program and never clear the WDT in the interrupt routine.

The max period of WDT =(TB1OV cycle time) * 8

S-7: Low Voltage Reset (LVR)

The low voltage reset (LVR) forces the MCU in reset state during power

failure, especially as MCU working in AC power application, preventing from

abnormal state is the key issue. The control bit LVREN is in independent

select always on or control by register by metal trim and LVR voltage is 2.2V.

WDT

Overflow

TFF

POR+RESET

SLEEP

INTF write $F first then

Write $303H after

DFF

TB1OV

as clock

Figure: Watch Dog Timer control circuit

Write INTF first &

Write $303H after

TTP258 Datasheet(PDF) 13 Page - Tontek Design Technology