1.8
EZ-USB Transfer Types
USB defines four transfer types. These match the requirements of different data types
delivered over the bus. (Section 1.13, "EZ-USB Endpoints" explains how the EZ-USB
family supports the four transfer types.)
1.8.1 Bulk Transfers
D
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0
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O
U
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Payload
Data
Payload
Data
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
H/S Pkt
Figure 1-4. Two Bulk Transfers, IN and OUT
Bulk data is bursty, traveling in packets of 8, 16, 32, or 64 bytes. Bulk data has guaranteed
accuracy, due to an automatic re-try mechanism for erroneous data. The host schedules
bulk packets when there is available bus time. Bulk transfers are typically used for printer,
scanner, or modem data. Bulk data has built-in flow control provided by handshake pack-
ets.
1.8.2 Interrupt Transfers
D
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1
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Payload
Data
6
Token Packet
Data Packet
H/S Pkt
Figure 1-5. An Interrupt Transfer
Interrupt data is like bulk data, but exists only for IN endpoints in the “Universal Serial
Bus Specification Version 1.1.” Interrupt data can have packet sizes of 1-64 bytes. Inter-
rupt endpoints have an associated polling interval that ensures that they will be pinged
(will receive an IN token) by the host on a regular basis.
EZ-USB TRM v1.9
Chapter 1. Introducing EZ-USB
Page 1-7
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