PIC18F2450/4450
Figure 14-8 shows the interrupt logic for the USB
module. There are two layers of interrupt registers in
the USB module. The top level consists of overall USB
status interrupts; these are enabled and flagged in the
UIE and UIR registers, respectively. The second level
consists of USB error conditions, which are enabled
and flagged in the UEIR and UEIE registers. An
interrupt condition in any of these triggers a USB Error
Interrupt Flag (UERRIF) in the top level.
14.5 USB Interrupts
The USB module can generate multiple interrupt
conditions. To accommodate all of these interrupt
sources, the module is provided with its own interrupt
logic structure, similar to that of the microcontroller.
USB interrupts are enabled with one set of control
registers and trapped with a separate set of flag regis-
ters. All sources are funneled into a single USB inter-
rupt
request,
USBIF
(PIR2<5>),
in
the
Interrupts may be used to trap routine events in a USB
transaction. Figure 14-9 shows some common events
within a USB frame and their corresponding interrupts.
microcontroller’s interrupt logic.
FIGURE 14-8:
USB INTERRUPT LOGIC FUNNEL
Top Level USB Interrupts
Second Level USB Interrupts
(USB Status Interrupts)
(USB Error Conditions)
UIR (Flag) and UIE (Enable) Registers
UEIR (Flag) and UEIE (Enable) Registers
SOFIF
SOFIE
BTSEF
BTSEE
TRNIF
TRNIE
USBIF
BTOEF
BTOEE
IDLEIF
IDLEIE
DFN8EF
DFN8EE
UERRIF
UERRIE
CRC16EF
CRC16EE
STALLIF
STALLIE
CRC5EF
CRC5EE
PIDEF
PIDEE
ACTVIF
ACTVIE
URSTIF
URSTIE
FIGURE 14-9:
EXAMPLE OF A USB TRANSACTION AND INTERRUPT EVENTS
To Host
ACK
From Host
From Host
Data
Set TRNIF
Set TRNIF
Set TRNIF
SETUPToken
From Host
IN Token
To Host
Data
From Host
ACK
USB Reset
URSTIF
From Host
From Host
To Host
ACK
START-OF-FRAME
OUT Token Empty Data
Transaction
SOFIF
Transaction
Complete
SOF
RESET
Differential Data
SOF
SETUP
DATA
STATUS
Control Transfer(1)
1 ms Frame
Note 1:
The control transfer shown here is only an example showing events that can occur for every transaction. Typical control transfers
will spread across multiple frames.
© 2006 Microchip Technology Inc.
Advance Information
DS39760A-page 143
MICROCHIP [ MICROCHIP ]
