UPSD3422 datasheet(156/293 Pages) STMICROELECTRONICS

156 / 293 page

USB interface

uPSD34xx

156/293

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 72

Table 72.

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

SUSPEND

EOPIE

RESUMIE

Bit

Symbol

R/W

Definition

–

Reserved

–

Reserved

–

Reserved

–

Reserved

RSTIE

R/W

Enable the USB Reset interrupt

SUSPEND

R/W

Enable the USB Suspend interrupt

EOPIE

R/W

Enable the USB EOP interrupt

RESUMIE

R/W

Enable the USB Resume interrupt

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