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38 • Watchdog Timer
5.1.2 GPIO Control Registers
There are two GPIOs on Nupro-850 that relate to watchdog timer. They are
listed below. The GPIO control base port is 480H.
WDT_TOUT# pin selection
WDT_TOUT# signal is multiplexed with GPIO32. When using WDT, this signal
must be switched to WDT_TOUT# function. It used bit 0 of GPIOBASE + 30H
to set WDT_TOUT function. (0 = WDT_TOUT#, 1 = GPIO32)
WDT LED Control
GPO25 of 6300ESB is designed to control WDT LED. Two features of WDT
LED are supported on Nupro-850’s WDT LED lights or blinks.
WDT LED light
Set bit 25 of GPIOBASE + 04H to 0. Bit 25 of GPIOBASE + 0CH determines
the state of WDT LED. (0 = light, 1 = dark)
WDT LED blink
Set bit 25 of GPIOBASE + 04H to 0. Bit 25 of GPIOBASE + 18H enables WDT
LED blinking function. (0 = function normally, 1 = enable blinking) The high and
low times have approximately 0.5 seconds each.
5.1.3 The procedure of programming WDT
Step 1: Make sure WDT_TOUT# signal is workable. (Not GPIO32 function).
Step 2: Set WDT output enable, presecaler and interrupt type into WDT
configuration register.
Step 3: Get control base from Base Address register.
Step 4: Program Preload register’s value according to unlocking sequence.
Step 5: Set WDT timer mode into WDT Lock Register.
Step 6: Enable WDT from WDT Lock register and program which
functionality of WDT LED will be.
To keep the timer from causing an interrupt or driving WDT_TOUT#, the timer
must be reloaded periodically. The frequency of reloads required is dependent
on the value of the preload values. To reload the down-counter, the register
unlocking sequence must be performed.
To disable WDT, Set bit 1 of WDT Lock Register to 0.