Full Speed USB


  • 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 (5 V), 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 5 V on D+ through a 1.5 KΩ pull-up resistor.

Frame Size and Transfer Types

FULL SPEED Frame size: 1 ms
Size of
per frame
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

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 state Differential "1"
Data K State Differential "0"
Idle Data J
Resume Data 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
Disconnect SE0 >= 2 μs
Connect Idle for 2.5 μs
Reset SE0 >= 2 μs

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