UPSD3422_06 Datasheet, PDF (147/293 Pages) STMicroelectronics – Turbo Plus Series Fast Turbo 8032 MCU with USB and Programmable Logic

uPSD34xx
USB interface
25.2
Note:
Types of transfers
The USB specification defines four types of transfers, Bulk, Interrupt, Isochronous, and
Control.
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
IN ADDR ENDP CRC5
Token Packet
Data1
Payload
Data
Data Packet
CRC16
ACK
Handshake Packet
OUT ADDR ENDP CRC5
Token Packet
Data1
Payload
Data
Data Packet
CRC16
ACK
Handshake Packet
AI10490
Figure 52. Interrupt Transfer
IN ADDR ENDP CRC5
Token Packet
Data1
Payload
Data
Data Packet
CRC16
ACK
Handshake Packet
AI10491
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