Motorola IH5, MCPN750A manual Raven Watchdog Timers, M48T559 Watchdog Timer

Block Diagram

Raven Watchdog Timers

The Raven ASIC contains two Watchdog timers, WDT1 and WDT2. Each timer is functionally equivalent but independent. These timers will continuously decrement until they reach a count of 0 or are reloaded by software. The timeout period is programmable from 1 microsecond up to 1024 milliseconds. There is an additional 4.8 second delay for each timer output provided by an external PLD. If the timer count reaches 0, a timer output signal will be asserted. The output of Watchdog Timer 1 an MPIC interrupt. The output of Watchdog Timer 2 is logically ORed onboard to provide a hard reset.

Following a device reset, WDT1 is enabled with a default timeout of 512 milliseconds and WDT2 is enabled with a default timeout of 576 milliseconds. Each of these signals is typically delayed an additional 4.8 seconds (2 seconds minimum) using logic external to Raven. Each timer must be disabled or reloaded by software to prevent a timeout. Software may reload a new timer value or force the timer to reload a previously loaded value. To disable or load/reload a timer requires a two step process. The first step is to write the pattern $55 to the timer register key field which will arm the timer register to enable an update. The second step is to write the pattern $AA to the key field along with the new timer information. During the power-up configuration of the Raven ASIC, PPCBug disables the two Watchdog timers.

M48T559 Watchdog Timer

The M48T559 contains one Watchdog timer. The reset output of the Watchdog timer is logically ORed into the reset logic and will generate a hard reset if the reset output is enabled and the timer expires. If the interrupt output is enabled, the Watchdog timer will generate an RTC interrupt if the timer expires. Refer to the device data sheet and the MCPN750A CompactPCI Single Board Computer Programmer’s Reference Guide (MCPN750A/PG) for programming information.

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