P89LV51RD2BA PHILIPS [NXP Semiconductors], P89LV51RD2BA Datasheet - Page 45

• Manufacturer Part Number: P89LV51RD2BA
• Description: 8-bit 80C51 3 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 14342
Product data
Fig 20. Block diagram of programmable Watchdog timer
external RST
7.7 Watchdog timer
CLK (XTAL1)
The device offers a programmable Watchdog Timer (WDT) for fail safe protection
against software deadlock and automatic recovery.
To protect the system against software deadlock, the user software must refresh the
WDT within a user-defined time period. If the software fails to do this periodical
refresh, an internal hardware reset will be initiated if enabled (WDRE = 1). The
software can be designed such that the WDT times out if the program does not work
properly.
The WDT in the device uses the system clock (XTAL1) as its time base. So strictly
speaking, it is a Watchdog counter rather than a Watchdog timer. The WDT register
will increment every 344,064 crystal clocks. The upper 8-bits of the time base register
(WDTD) are used as the reload register of the WDT.
The WDTS flag bit is set by WDT overflow and is not changed by WDT reset. User
software can clear WDTS by writing ‘1' to it.
Figure 20
control Watchdog timer operation. During idle mode, WDT operation is temporarily
suspended, and resumes upon an interrupt exit from idle.
The time-out period of the WDT is calculated as follows:
where WDTD is the value loaded into the WDTD register and f
frequency.
Table 35:
Bit addressable; Reset value: 00H
Bit
Symbol
Period = (255
WDTC
COUNTER
provides a block diagram of the WDT. Two SFRs (WDTC and WDTD)
WDTC - Watchdog control register (address COH) bit allocation
7
-
Rev. 04 — 02 December 2004
WDTD)
344064
clks
6
-
UPPER BYTE
344064
WDTD
WDT
5
-
P89LV51RB2/RC2/RD2
WDOUT
1/f
WDT reset
CLK (XTAL1)
4
8-bit microcontrollers with 80C51 core
002aaa531
WDRE
3
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
internal reset
WDTS
2
osc
is the oscillator
WDT
1
SWDT
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