UPSD3422 datasheet(147/293 Pages) STMICROELECTRONICS

147 / 293 page

uPSD34xx

USB interface

147/293

25.2

Types of transfers

The USB specification defines four types of transfers, Bulk, Interrupt, Isochronous, and

Control.

Note:

The uPSD34xx supports all types of transfers except Isochronous.

●

Bulk Transfers (see Figure 51)

Bulk data is transferred in both directions and is used with both IN and OUT endpoints.

Packets may be 8, 16, 32, or 64 bytes in length. Bulk transfers occur in bursts, and are

scheduled by the host when there is available time on the bus. While there is no

guaranteed delivery time for bulk transfers, the accuracy of the data is guaranteed due

to automatic retries for erroneous data. Bulk transfers are typically used for mass

storage, printer, and scanner data.

●

Interrupt Transfers (see Figure 52)

Interrupt data is a lot like bulk data but travels only in one direction, from the device to

the host, so only IN endpoints are used. Interrupt data holds packet sizes ranging from

1 to 64 bytes. Interrupt endpoints have an associated polling interval, meaning that the

host sends IN tokens at a periodic interval to the host on a regular basis. Interrupt

transfers are typically used for human interface devices such as keyboards, mice, and

joysticks.

Figure 51.

IN and OUT Bulk Transfers

Figure 52.

Interrupt Transfer

Token Packet

Data Packet

Handshake Packet

ADDR

ENDP

CRC5

CRC16

ACK

Data1

Payload

Data

Token Packet

Data Packet

Handshake Packet

OUT

ADDR

ENDP

CRC5

CRC16

ACK

Data1

Payload

Data

AI10490

Token Packet

Data Packet

Handshake Packet

ADDR

ENDP

CRC5

CRC16

ACK

Data1

Payload

Data

AI10491

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