USB Frames

USB data transfers occur through a series of events called transactions. Transactions are conducted within a host-controlled time interval called a frame. The length and frequency of the transactions depend upon the transfer type being used for an endpoint.

The type of transfer which can be sent in a frame and the frame length is defined by the specified speed of the USB.

The four possible USB transfer types allowed are:

Frame Specifications

LOW SPEED Frame size: 1 ms
Supported
Transfer
Types		 Maximum
Size of
Transfer		 Transfers
per frame		 Maximum
Theoretical
Throughput
Control 8 bytes 1 8 K bytes/sec
Interrupt 8 bytes 1 8 K bytes/sec
Bulk - 0 -
Isochronous - 0 -
FULL SPEED Frame size: 1 ms
Supported
Transfer
Types		 Maximum
Size of
Transfer		 Transfers
per frame		 Maximum
Theoretical
Throughput
Control 64 bytes 1 64 kbytes/s
Interrupt 64 bytes 1 64 kbytes/s
Bulk 64 bytes Up to 19 1.2 Mbytes/s
Isochronous 1023 bytes 1 1023 kbytes/s

HIGH SPEED Frame size: 125 μs

Supported
Transfer
Types		 Maximum
Size of
Transfer		 Transfers
per frame		 Maximum
Theoretical
Throughput
Control 64 bytes 1 64 kByte/s
Interrupt 1024 bytes up to 3 24 MByte/s
Bulk 512 bytes up to 13 53 MByte/s
Isochronous 1024 bytes up to 3 24 MByte/s

  Return to Top

© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.