UPSD3422_V01 datasheet(162/300 Pages) STMICROELECTRONICS

162 / 300 page

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UPSD3422, UPSD3433, UPSD3434, UPSD3454

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25.4.2

Endpoint FIFO pairing

Endpoint FIFOs can be paired for double buffering to provide an efficient method for bulk

data transfers. With double buffering enabled, the MCU can operate on one data packet

while another is being transferred over USB.

When two FIFOs are paired, the active FIFO is automatically toggled by the update of

USIZE. The MCU must only use the odd numbered endpoint FIFO when paired in order to

access the active FIFO. For example, if endpoints 3 and 4 OUT FIFOs are paired, the active

FIFO is accessed via endpoint 3’s OUT FIFO (see Table 102).

Table 100.

USB device address register (UADDR 0E2h, reset value 00h)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

–

USBADDR[6:0]

Table 101.

UADDR register bit definition

Bit

Symbol

R/W

Definition

–

Reserved

6:0

USBADDR

R/W

USB Address of the device.

These bits are cleared with a Hardware RESET. When a USB

RESET is detected, the address register should be cleared.

Table 102.

Pairing control register (UPAIR 0E3h, reset value 00h)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

–

PR3OUT

PR1OUT

PR3IN

PR1IN

Table 103.

UPAIR register bit definition

Bit

Symbol

R/W

Definition

–

Reserved

–

Reserved

–

Reserved

–

Reserved

3PR3OUT

R/W

Setting this bit enables double buffering of the OUT FIFOs for

Endpoints 3 and 4. Access to the double buffered FIFOs is

through Endpoint3’s OUT FIFO.

2PR1OUT

R/W

Setting this bit enables double buffering of the OUT FIFOs for

Endpoints 1 and 2. Access to the double buffered FIFOs is

through Endpoint1’s OUT FIFO.

1PR3IN

R/W

Setting this bit enables double buffering of the IN FIFOs for

Endpoints 3 and 4. Access to the double buffered FIFOs is

through Endpoint3’s IN FIFO.

0PR1IN

R/W

Setting this bit enables double buffering of the IN FIFOs for

Endpoints 1 and 2. Access to the double buffered FIFOs is

through Endpoint1’s IN FIFO.

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UPSD3422 Datasheet(PDF) 162 Page - STMicroelectronics

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