UPSD3422EB40U6 datasheet(163/300 Pages) STMICROELECTRONICS

163 / 300 page

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UPSD3422, UPSD3433, UPSD3434, UPSD3454

USB interface

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25.4.3

USB interrupts

There are many USB related events that generate an interrupt. The events that generate an

interrupt are selectively enabled through the use of the USB interrupt enable registers. All

USB interrupts are serviced through a single interrupt vector (see Section 13: Interrupt

system on page 62 for the address of the interrupt vector). When a USB interrupt occurs,

firmware must check the USB interrupt flag registers to determine the source of the

interrupt, clear that interrupt flag and process the interrupt before returning to the interrupted

code.

The USB interrupt priority can be set to low or high. For the best USB response time and to

maximize data transfer times, the USB interrupt should be set to the highest priority (see the

Section 13: Interrupt system for the details on setting the interrupt priority).

●

USB Reset Interrupt

The host signals a bus reset by driving both D+ and D– low for at least 10ms. When

the UPSD34xx’s SIE detects a reset on the USB, it generates the RST interrupt

request. A USB reset does not reset the CPU nor the USB SIE, nor does it disable the

USB SIE. The interrupt service routine should disable/enable the USB SIE to reset a

portion of the state machine and initialize the USB SIE registers per the application

requirements.

●

USB Suspend Interrupt

If the UPSD34xx’s SIE detects 3ms of no activity on the bus, it generates the

SUSPEND interrupt request. It also causes the clock to the SIE to shut down to

conserve power.

●

USB EOP (End of Packet) Interrupt

Every packet sent on the USB includes a signal, called EOP, to indicate the end of the

packet. When an EOP is detected, the SIE generates an EOP interrupt.

●

USB Resume Interrupt

When USB activity is detected and the SIE is in the suspend state, a RESUME

interrupt is generated. The USB Resume interrupt service routine should clear the

SUSPENDF bit in the UIF0 register if it is set in order to turn the USB SIE clock on.

●

USB global interrupt enable register (UIE0)

There are four USB events that are considered to be global in nature, meaning they are

not specific to an endpoint, but apply to the USB bus in general. The four global USB

events include Reset, Suspend, EOP, and Resume.

Each event can be enabled to generate an interrupt using the UIE0 register shown in

Table 104

Table 104.

USB global interrupt enable register (UIE0 0E4h, reset value 00h)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

–

RSTIE

SUSPENDIE

EOPIE

RESUMIE

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