PIC18F4550ESPQTP datasheet(184/438 Pages) MICROCHIP

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PIC18F2455/2550/4455/4550

DS39632E-page 182

17.5.1.1

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 flag as shown in Example 17-1.

EXAMPLE 17-1:

CLEARING ACTVIF BIT (UIR<2>)

Note:

Only one ACTVIF interrupt is generated

when resuming 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.

Assembly:

BCF

UCON, SUSPND

Loop:

BCF

UIR, ACTVIF

BTFSC UIR, ACTVIF

BRA

Loop

Done:

UCONbits.SUSPND = 0;

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

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