PIC18F44J50-I Datasheet, PDF (374/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
22.5.1.1 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 provided in Example 22-1.
Note:
Only one ACTVIF interrupt is generated
when resuming from the USB bus Idle con-
dition. 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 22-1: CLEARING ACTVIF BIT (UIR<2>)
Assembly:
BCF
LOOP:
BTFSS
BRA
BCF
BRA
DONE:
UCON, SUSPND
UIR, ACTVIF
DONE
UIR, ACTVIF
LOOP
C:
UCONbits.SUSPND = 0;
while (UIRbits.ACTVIF) { UIRbits.ACTVIF = 0; }
DS39931D-page 374
 2011 Microchip Technology Inc.