User manual

PCA-6742 User Manual 36
B.1.2 Example Program
1. Enable watchdog timer and set 10 sec. as timeout interval
;-----------------------------------------------------------
Mov dx,2eh ; Unlock W83627HG
Mov al,87h
Out dx,al
Out dx,al
;-----------------------------------------------------------
Mov al,07h ; Select registers of watchdog timer
Out dx,al
Inc dx
Mov al,08h
Out dx,al
;-----------------------------------------------------------
Dec dx ; Enable the function of watchdog timer
Mov al,30h
Out dx,al
Inc dx
Mov al,01h
Out dx,al
;-----------------------------------------------------------
Table B.1: Watchdog timer registers
Address of
register (2E)
Attribute
Read/Write
Value (2F)& description
87 (hex) -----
Write this address to I/O address port 2E (hex) twice to
unlock the W83627HG
07 (hex) write Write 08 (hex) to select register of watchdog timer.
30 (hex) write
Write 01 (hex) to enable the function of the watchdog timer.
Disabled is set as default.
F5 (hex) write
Set seconds or minutes as units for the timer. Write 0 to bit 3:
set second as counting unit. [default]. Write 1 to bit 3: set
minutes as counting unit
F6 (hex) write
0: stop timer [default]
01~FF (hex): The amount of the count, in seconds or min-
utes, depends on the value set in register F5 (hex). This
number decides how long the watchdog timer waits for
strobe before generating an interrupt or reset signal. Writing
a new value to this register can reset the timer to count with
the new value.
F7 (hex) read/write
Bit 6: Write 1 to enable keyboard to reset the timer, 0 to dis-
able.[default]
Bit 5: Write 1 to generate a timeout signal immediately and
automatically return to 0. [default=0]
Bit 4: Read status of watchdog timer, 1 means timer is “time-
out”.
AA (hex) -----
Write this address to I/O port 2E (hex) to lock the watchdog
timer 2.