STFPC320 datasheet(17/78 Pages) STMICROELECTRONICS

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STFPC320

Functional description

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4.5

Interrupts/events handling by STFPC320

The STFPC320 interrupts the Host by pulling the IRQ_N/SQW pin to a low-level both in

normal mode of operation and during wake-up. The interrupt is enabled by STFPC320 when

any of the conditions occur:

●

Front panel key press in normal operation or during system standby state

●

Remote control key press in normal operation or during system standby state

●

A low-to-high transition on the external pin, PIN_AV8

●

Real-time clock triggers (alarm, watchdog timer, oscillator fail)

The IRQ_N/SQW is an active low level signal and is cleared only after the interrupt buffer is

read. After reading the interrupt buffer, the Host will know the actual source of the interrupt.

This allows the Host to exactly know the event which caused the interrupt (e.g STBY key on

the front panel). The interrupt signal is used to inform the Host of any events detected by the

STFPC320. Note that the IRQ_N/SQW pin is an open-drain pin which requires an external

pull-up resistor.

4.6

Ready pin

The STFPC320 supports cutting-off power to the main board for standby operation for good

power management. STBY will be set to high when the READY transitions from high to low.

During a cold boot up or wakeup from standby, if the READY pin stays low, the STFPC320

will assert the STBY when the guard timer has finished counting down to 0.

When the READY drops to a low, MUTE goes high immediately and soon after (2 µs) the

STBY is asserted.

In the normal mode of operation, when READY is a high, the STBY is asserted only when

the guard timer is enabled and has finished counting down to 0. This is meant to put the

system into standby as the READY pin was stuck at high and the guard timer register was

not cleared before it finished counting down to 0. It is advised to disable the guard timer

during normal operation.

Figure 7.

Interrupts/events handling

STFPC320 Datasheet(PDF) 17 Page - STMicroelectronics