Philips P89LPC908, P89LPC906 Watchdog Function, Watchdog timer configuration, Wdte Wdse Function

Page 79

Philips Semiconductors

User’s Manual - Preliminary -

 

 

 

WATCHDOG TIMER

P89LPC906/907/908

12. WATCHDOG TIMER

 

 

The watchdog timer subsystem protects the system from incorrect code execution by causing a system reset when it underflows as a result of a failure of software to feed the timer prior to the timer reaching its terminal count. The watchdog timer can only be reset by a power-on reset.

WATCHDOG FUNCTION

The user has the ability using the WDCON and UCFG1 registers to control the run /stop condition of the WDT, the clock source for the WDT, the prescaler value, and whether the WDT is enabled to reset the device on underflow. In addition, there is a safety mechanism which forces the WDT to be enabled by values programmed into UCFG1 either through IAP or a commercial programmer.

The WDTE bit (UCFG1.7), if set, enables the WDT to reset the device on underflow. Following reset, the WDT will be running regardless of the state of the WDTE bit.

The WDRUN bit (WDCON.2) can be set to start the WDT and cleared to stop the WDT. Following reset this bit will be set and the WDT will be running. All writes to WDCON need to be followed by a feed sequence (see section "Feed Sequence" on page 80). Additional bits in WDCON allow the user to select the clocksource for the WDT and the prescaler.

When the timer is not enabled to reset the device on underflow, the WDT can be used in "timer mode" and be enabled to produce an interrupt (IEN0.6) if desired.

The Watchdog Safety Enable bit, WDSE (UCFG1.4) along with WDTE, is designed to force certain operating conditions at power- up. Refer to the Table for details

Table 12-1: .Watchdog timer configuration

WDTE

WDSE

 

FUNCTION

(UCFG1.7)

(UCFG1.4)

 

 

 

 

 

 

0

x

The watchdog reset is disabled. The timer can be used as an internal timer and

can be used to generate an interrupt. WDSE has no effect.

 

 

 

 

 

1

0

The watchdog reset is enabled. The user can set WDCLK to choose the clock

source.

 

 

 

 

 

 

 

The watchdog reset is enabled, along with additional safety features:

1

1

1.

WDCLK is forced to 1 (using watchdog oscillator)

2.

WDCON and WDL register can only be written once

 

 

 

 

3.

WDRUN is forced to 1and cannot be cleared by software.

 

 

 

 

Figure 12-3 shows the watchdog timer in watchdog mode. It consists of a programmable 13-bit prescaler, and an 8-bit down counter. The down counter is clocked (decremented) by a tap taken from the prescaler. The clock source for the prescaler is either PCLK or the watchdog oscillator selected by the WDCLK bit in the WDCON register. (Note that switching of the clock sources will not take effect immediately - see section "Watchdog Clock Source" on page 84).

The watchdog asserts the watchdog reset when the watchdog count underflows and the watchdog reset is enabled. When the watchdog reset is enabled, writing to WDL or WDCON must be followed by a feed sequence for the new values to take effect.

If a watchdog reset occurs, the internal reset is active for at least one watchdog clock cycle (PCLK or the watchdog oscillator clock). If CCLK is still running, code execution will begin immediately after the reset cycle. If the processor was in Power down mode, the watchdog reset will start the oscillator and code execution will resume after the oscillator is stable.

2003 Dec 8

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Contents User Manual Table of Contents Power-On reset code execution Brownout Detection Power-On Detection Power Reduction Modes103 List of Figures List of Figures P89LPC906 PIN ConfigurationsProduct Comparison Logic SymbolsOscillator Divider Block Diagram P89LPC906KB Code Flash CPUClock Block Diagram P89LPC907Uart Byte Data RAMData RAM Port Block Diagram P89LPC908PIN Descriptions P89LPC906 P1.2 PIN Descriptions P89LPC907P1.0 TxDRxD PIN Descriptions P89LPC908Keyboard Input P1.0 P1.5 P1.1Special function registers table P89LPC906 Special function registersMSB LSB Hex Special function registers table P89LPC907 CMP1 Cmpref TRIM.5 TRIM.4 TRIM.3 TRIM.2 TRIM.1 TRIM.0 WDCON# Special function registers table P89LPC908 KB2 KB6 KB5 KB4 TL0 Code Memory OrganizationData SFRLOW Speed Oscillator Option P89LPC906 Enhanced CPUClock Definitions CPU Clock OscclkWatchdog Oscillator Option Oscillator Option SELECTION- P89LPC906Clock Output P89LPC906 ON-CHIP RC Oscillator OptionCPU Clock Cclk Modification Divm Register CPU Clock Cclk Wakeup DelayBIT Symbol Function External Clock Input Option P89LPC906Low freq LOW Power Select P89LPC906High freq Med freqCPU Clocks Interrupt Arbitration Flag Bits Address Enable Bits Priority RankingInterrupt Priority Structure Summary of Interrupts P89LPC906 DescriptionTI & RI External Interrupt InputsExternal Interrupt PIN Glitch Suppression Summary of Interrupts P89LPC907,P89LPC908 DescriptionBopd EBO Rtcf Kbif Interrupts RST Port ConfigurationsQUASI-BIDIRECTIONAL Output Configuration Number of I/O Pins Available Clock Source Reset OptionPort latch data Open Drain Output ConfigurationStrong Port latch data Port pin Input data Glitch rejection INPUT-ONLY ConfigurationPUSH-PULL Output Configuration Port 0 Analog FunctionsPort Output Configuration P89LPC907 Port Output Configuration P89LPC906Port Output Configuration P89LPC908 Ports Ports TMOD.3 TmodTMOD.7 TMOD.6TAMOD.7-1 Overflows. ModeMode Tamod P89LPC907Tcon THn TFn PclkT0C/T = Overflow TLn THn TFn Interrupt T0 Pin T0C/T = OverflowPclk TL0 Timer Overflow Toggle Output P89LPC907TR0 ENT0 Pclk TH0 Timers 0 REAL-TIME Clock Source Divm Cclk FOSC2 FOSC1 FOSC0 RTCS10UCFG1.2 UCFG1.1 UCFG1.0 Cclk Frequency RTC Clock Frequency XclkExternal clock/DIVM RC Oscillator/DIVMWDT Oscillator/DIVM UndefinedChanging RTCS1-0 Reset Sources Affecting the REAL-TIME ClockREAL-TIME Clock INTERRUPT/WAKE UP Rtccon REAL-TIME CLOCK/SYSTEM Timer Brownout Detection Power Reduction Modes POWER-ON DetectionBrownout Options Power Reduction Modes Pcon Pcona Power Monitoring Functions Modes UartSFR Locations for UARTs SFR SpaceBaud Rate Generator and Selection Updating the BRGR1 and BRGR0 SfrsBreak Detect Framing ErrorBrgcon Scon Sstat More about Uart ModeSerial Port Mode 0 Double Buffering Must Be Disabled PCON.6 RB8 SMOD0 Framing Error and RI in Modes 2 and 3 with SM2 =FE and RI when SM2 = 1 in Modes 2 More about Uart Modes 2Double Buffering in Different Modes Double BufferingTransmission with and without Double Buffering 9TH BIT BIT 8 in Double Buffering Modes 1, 2Automatic Address Recognition Multiprocessor CommunicationsUart Uart Block Diagram of Reset POWER-ON Reset Code ExecutionRstsrc Comparator Configuration CIN1A CO1 CMP1 Cmpref Comparator and Power Reduction ModesInternal Reference Voltage Comparator InterruptComparator Configuration Example Analog Comparators Kbcon KbpatnKbmask Watchdog Function Watchdog timer configurationWdte Wdse Function Feed Sequence Wdcon PRE2-PRE0 P89LPC906/907/908 Watchdog Timeout ValuesControl register Watchdog Timer in Timer ModePrescaler Reset Pclk WatchdogCLK Power Down OperationWatchdog Clock Source PrescalerWatchdog Timer Watchdog Timer Dual Data Pointers Software ResetAUXR1 MOVX@DPTR, a MOVCA, @A+DPTRMove code byte relative to Dptr to the accumulator MOVXA, @DPTRIntroduction to IAP-LITE FeaturesUsing Flash AS Data Storage General DescriptionFlash Program Memory Fmcon Assembly language routine to erase/program all or part of a Accessing Additional Flash ElementsReading Additional Flash Elements ERASE-PROGRAMMING Additional Flash ElementsUCFG1 Fmadrl Conf UCFG1 User Configuration BytesP89LPC906 Unprogrammed value 00h User Security BytesSECx Address xxxxhBootstat BootvecLogical ArithmeticData Transfer Mnemonic Description Bytes Cycles Hex CodeBranching BooleanMiscellaneous RetiB8-BF D8-DF2003 Dec Initial release 104 Index Dual Data Pointers Port 0 12, 13 SFR 109 P89LPC906/907/908
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