Datasheet

PIC18F2450/4450

14.5.1.1 Bus Activity Detect Interrupt Bit

(ACTVIF)

The ACTVIF bit cannot be cleared immediately after

the USB module wakes up from Suspend or while the

USB module is suspended. A few clock cycles are

required to synchronize the internal hardware state

machine before the ACTVIF bit can be cleared by

firmware. Clearing the ACTVIF bit before the internal

hardware is synchronized may not have an effect on

the value of ACTVIF. Additionally, if the USB module

uses the clock from the 96 MHz PLL source, then after

clearing the SUSPND bit, the USB module may not be

immediately operational while waiting for the 96 MHz

PLL to lock. The application code should clear the

ACTVIF bit as shown in Example 14-1.

Only one ACTVIF interrupt is generated when resum-

ing from the USB bus Idle condition. If user firmware

clears the ACTVIF bit, the bit will not immediately

become set again, even when there is continuous bus

traffic. Bus traffic must cease long enough to generate

another IDLEIF condition before another ACTVIF

interrupt can be generated.

EXAMPLE 14-1: CLEARING ACTVIF BIT

(UIR<2>)

Assembly:

BCF UCON, SUSPND

LOOP:

BTFSS UIR, ACTVIF

BRA DONE

BCF UIR, ACTVIF

BRA LOOP

DONE

UCONbits.SUSPND = 0;

while (UIRbits.ACTVIF){UIRbits.ACTVIF = 0};