8XC54 Datasheet, PDF (32/56 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 8K-4K/256-1K OTP/ROM/ROMless, low voltage (2.7V-5.5V), low power, high speed (33 MHz)

Philips Semiconductors
80C51 8-bit microcontroller family
8K–64K/256–1K OTP/ROM/ROMless, low voltage (2.7V–5.5V),
low power, high speed (33MHz)
Product specification
8XC54/58
8XC51FA/FB/FC/80C51FA
8XC51RA+/RB+/RC+/RD+/80C51RA+
(8XC51FX and 8XC51RX+ ONLY)
INIT_WATCHDOG:
MOV CCAPM4, #4CH
; Module 4 in compare mode
MOV CCAP4L, #0FFH
; Write to low byte first
MOV CCAP4H, #0FFH
; Before PCA timer counts up to
; FFFF Hex, these compare values
; must be changed
ORL CMOD, #40H
; Set the WDTE bit to enable the
; watchdog timer without changing
; the other bits in CMOD
;
;********************************************************************
;
; Main program goes here, but CALL WATCHDOG periodically.
;
;********************************************************************
;
WATCHDOG:
CLR EA
; Hold off interrupts
MOV CCAP4L, #00
; Next compare value is within
MOV CCAP4H, CH
; 255 counts of the current PCA
SETB EA
; timer value
RET
Figure 26. PCA Watchdog Timer Initialization Code
2000 Aug 07
32