P89C51RC2BASLASH01 datasheet(43/68 Pages) PHILIPS

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Philips Semiconductors

Preliminary data

P89C51RA2/RB2/RC2/RD2xx

80C51 8-bit Flash microcontroller family

8KB/16KB/32KB/64KB ISP/IAP Flash with 512B/512B/512B/1KB RAM

2002 Jul 18

ERAM

256 or 768 BYTES

UPPER

128 BYTES

INTERNAL RAM

LOWER

128 BYTES

INTERNAL RAM

SPECIAL

FUNCTION

100

EXTERNAL

DATA

MEMORY

FFFF

0000

SU01293

Figure 39. Internal and External Data Memory Address Space with EXTRAM = 0

HARDWARE WATCHDOG TIMER (ONE-TIME

ENABLED WITH RESET-OUT FOR

P89C51RA2/RB2/RC2/RD2xx)

The WDT is intended as a recovery method in situations where the

CPU may be subjected to software upset. The WDT consists of a

14-bit counter and the WatchDog Timer reset (WDTRST) SFR. The

WDT is disabled at reset. To enable the WDT, the user must write

01EH and 0E1H in sequence to the WDTRST, SFR location 0A6H.

When the WDT is enabled, it will increment every machine cycle

while the oscillator is running and there is no way to disable the

WDT except through reset (either hardware reset or WDT overflow

reset). When the WDT overflows, it will drive an output reset HIGH

pulse at the RST-pin (see the note below).

Using the WDT

To enable the WDT, the user must write 01EH and 0E1H in sequence

to the WDTRST, SFR location 0A6H. When the WDT is enabled, the

user needs to service it by writing 01EH and 0E1H to WDTRST to

avoid a WDT overflow. The 14-bit counter overflows when it reaches

16383 (3FFFH) and this will reset the device. When the WDT is

enabled, it will increment every machine cycle while the oscillator is

running. This means the user must reset the WDT at least every

16383 machine cycles. To reset the WDT, the user must write 01EH

and 0E1H to WDTRST. WDTRST is a write only register. The WDT

counter cannot be read or written. When the WDT overflows, it will

generate an output RESET pulse at the reset pin (see note below).

The RESET pulse duration is 98

× TOSC (6-clock mode; 196 in

12-clock mode), where TOSC = 1/fOSC. To make the best use of the

WDT, it should be serviced in those sections of code that will

periodically be executed within the time required to prevent a WDT

reset.

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