PIC18F4550ESOSQTP datasheet(179/430 Pages) MICROCHIP

179 / 430 page

Preliminary

DS39632D-page 177

PIC18F2455/2550/4455/4550

17.5

USB Interrupts

The USB module can generate multiple interrupt con-

ditions. 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 registers. All

sources are funneled into a single USB interrupt

request, USBIF (PIR2<5>), in the microcontroller’s

interrupt logic.

Figure 17-8 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.

Interrupts may be used to trap routine events in a USB

transaction. Figure 17-9 shows some common events

within a USB frame and their corresponding interrupts.

FIGURE 17-8:

USB INTERRUPT LOGIC FUNNEL

FIGURE 17-9:

EXAMPLE OF A USB TRANSACTION AND INTERRUPT EVENTS

BTSEF

BTSEE

BTOEF

BTOEE

DFN8EF

DFN8EE

CRC16EF

CRC16EE

CRC5EF

CRC5EE

PIDEF

PIDEE

SOFIF

SOFIE

TRNIF

TRNIE

IDLEIF

IDLEIE

STALLIF

STALLIE

ACTVIF

ACTVIE

URSTIF

URSTIE

UERRIF

UERRIE

USBIF

Second Level USB Interrupts

(USB Error Conditions)

UEIR (Flag) and UEIE (Enable) Registers

Top Level USB Interrupts

(USB Status Interrupts)

UIR (Flag) and UIE (Enable) Registers

USB Reset

SOF

RESET

SETUP

DATA

STATUS

SOF

SETUPToken

Data

ACK

OUT Token

Empty Data

ACK

START-OF-FRAME

IN Token

Data

ACK

SOFIF

URSTIF

1 ms Frame

Differential Data

From Host

To Host

From Host

To Host

From Host

To Host

Transaction

Control Transfer(1)

Transaction

Complete

Note

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.

Set TRNIF

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