Specification
- USB High Speed was introduced in 2000 as part of the USB 2.0 specification
- Maximum theoretical bandwidth is 480 Mbit/s
- 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 USB connectors.
Enumeration
High speed Devices begin the enumeration process identical to Full Speed Devices. High Speed Devices announce to the Host they are ready to be enumerated by asserting a 5 V signal on D+ through the use of a 1.5 kΩ pull-up resistor. During the 20 ms enumeration RESET signal sent by the Host, the Device executes the High Speed negotiation process. Upon completing this negotiation, the Device, Host and Hub port connecting the Device will operate in High Speed mode.
Differences from Full Speed USB
Microframes
High Speed USB was designed to coexist with Full Speed USB. The designers speculated many systems would have a Host which could simultaneously offer support for Full and High Speed Devices. To achieve compatibility 8 high speed "microframes' are completed within 1 ms.
Frame Size and Transfer Types
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 |
USB Bus States and Signal Levels
| HS USB 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 2 bits, followed by Data J for 1 bit |
| Disconnect | SE0 >= 2 μs |
| Connect | Idle for 2.5 μs |
| Reset | SE0 >= 2 μs |
