PIC18F2450_08 Datasheet, PDF (147/324 Pages) Microchip Technology – 28/40/44-Pin, High-Performance, 12 MIPS, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

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.
PIC18F2450/4450
EXAMPLE 14-1: CLEARING ACTVIF BIT
(UIR<2>)
Assembly:
LOOP:
DONE
BCF
BTFSS
BRA
BCF
BRA
UCON, SUSPND
UIR, ACTVIF
DONE
UIR, ACTVIF
LOOP
C:
UCONbits.SUSPND = 0;
while (UIRbits.ACTVIF){UIRbits.ACTVIF = 0};
© 2008 Microchip Technology Inc.
DS39760D-page 145