Full Speed USB

Last modified by Microchip on 2023/11/10 11:19


  • USB Full Speed mode was introduced in 1996 with the USB v1.0 specification (later revised to USB 1.1 1998)
  • Maximum theoretical bandwidth is 1.2 Mbits/sec
  • Uses four data lines - Power (5V), ground, and two data lines (D+ and D-)
  • Half-Duplex differential signaling on D+ and D-
  • Uses the traditional (i.e. defined before USB 3.0) USB connectors


Full Speed devices announce to a host that they are ready to be enumerated by asserting 5V on D+ through a 1.5 KΩ pull-up resistor.

Frame Size and Transfer Types

Full Speed Frame Size: 1 ms

Supported Transfer TypesMaximum Size of TransferTransfers per FrameMaximum Theoretical Throughput
Control64 bytes164 kbytes/s
Interrupt64 bytes164 kbytes/s
Bulk64 bytesUp to 191.2 Mbytes/s
Isochronous1023 bytes11023 kbytes/s

USB Bus States and Signal Levels

Bus States
Bus Levels
Differential "1"D+ high, D- low
Differential "0"D+ low, D- high
Single Ended 0 (SE0)D+ low, D- low
Single Ended 1 (SE1)D+ high, D- high Invalid condition!
Data J stateDifferential "1"
Data K StateDifferential "0"
IdleData J
ResumeData K
Start of Packet (SOP)Switches from Idle to Data K
End of Packet (EOP)SE0 for two bits, followed by Data J for one bit
DisconnectSE0 >= 2 μs
ConnectIdle for 2.5 μs
ResetSE0 >= 2 μs

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