The Eltron Company P310 manual USB Concerns

CHAPTER 2

USB Concerns

(USB Specification Rev. 2.0)

1.USB-Equipped Host Computers have Hub connection(s) and software that supports the connections for up to 127 devices (either USB Functions or USB Hubs), all hot swapable.

2.Hubs implement one connection path upstream to, or toward, the Host and typically several Ports for downstream Functions and/or other Hub connections. Functions refer to Printers, Mice, Keyboards, etc.

3.USB Cables each have both A- and B-type connectors. The A connectors attach to upstream devices, while the B connectors attach to downstream devices. Hub loopback connections (requiring an A-to-A cable) are not allowed.

4.System Software keeps track of the paths and path parameters both to and from Functions (as Pipes). System Software does not support more than five Hubs, not counting the host, along any path.

5.A Pipe can operate at USB High Speed (480Mb/s), USB Full Speed (12Mb/s), or USB Low Speed (1.5 Mb/s). Functions report needed parameters as part of setup phases during operations (e.g., following hot swaps).

6.USB Ports and Cables have a shield and four conductors—two for data and two that can supply 5 volts to Bus-Powered Devices.

7.It is important to have cables that can support the bandwidth requirements of a particular path. Low Speed Cables should not be used in paths that can also operate at High/Full Speeds.

8.Cable designers must meet specified requirements for data integrity between devices by using materials suitable for the lengths offered. Extension Cables can add factors that breach critical design elements and should not be used.

	A	End Views		B
4 3 2 1			2	1
			3	4

V Bus 1	1 V Bus
D+ 2	2 D+
D- 3	3 D-
Ground 4	4 Ground
Shield	Shield

Cable Wiring

Figure 2-9. USB Issues.

980264-001 Rev. B 2-7