LPC2131/2132/2138 User Manual - mct.net

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Philips Semiconductors Preliminary User Manual ARM-based Microcontroller Watchdog Feed Register (WDFEED - 0xE0000008) LPC2131/2132/2138 Writing 0xAA followed by 0x55 to this register will reload the Watchdog timer to the WDTC value. This operation will also start the Watchdog if it is enabled via the WDMOD register. Setting the WDEN bit in the WDMOD register is not sufficient to enable the Watchdog. A valid feed sequence must first be completed before the Watchdog is capable of generating an interrupt/ reset. Until then, the Watchdog will ignore feed errors. Once 0xAA is written to the WDFEED register the next operation in the Watchdog register space should be a WRITE (0x55) to the WDFFED register otherwise the Watchdog is triggered. The interrupt/ reset will be generated during the second pclk following an incorrect access to a watchdog timer register during a feed sequence. Table 170: Watchdog Feed Register (WDFEED - 0xE0000008) WDFEED Function Description Watchdog Timer Value Register (WDTV - 0xE000000C) The WDTV register is used to read the current value of Watchdog timer. Reset Value 7:0 Feed Feed value should be 0xAA followed by 0x55 undefined Table 171: Watchdog Timer Value Register (WDTV - 0xE000000C) WDTV Function Description Reset Value 31:0 Count Current timer value 0xFF Watchdog 222 November 22, 2004
Philips Semiconductors Preliminary User Manual ARM-based Microcontroller BLOCK DIAGRAM The block diagram of the Watchdog is shown below in the Figure 53. FEED SEQUENCE WDFEED pclk FEED ERROR FEED OK WDTV REGISTER / 4 CURRENT WD TIMER COUNT WDMOD REGISTER 1. Counter is enabled only when the WDEN bit is set and a valid feed sequence is done. 2. WDEN and WDRESET are sticky bits. Once set they can’t be cleared until the Watchdog underflows or an external reset occurs. WDTC 32-BIT DOWN COUNTER ENABLE COUNT 1 SHADOW BIT WDEN 2 UNDER FLOW WDTOF Figure 53: Watchdog Block Diagram WDINT LPC2131/2132/2138 WDRESET 2 RESET INTERRUPT Watchdog 223 November 22, 2004
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LPC2131/2132/2138 User Manual - mct.net

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