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Rev. 1.00
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SRP-F310/312
※ Note: Minimum conductor construction must be stranded tinned copper.
To minimize end user termination problems, USB uses a keyed connector protocol. The physical difference
in the Series A and B connectors insures proper end user connectivity. The A connector is the principle
means of connecting USB devices directly to a host or to the downstream port of a hub. All USB devices
must have the standard Series A connector specified in this chapter. The B connector allows device vendors
to provide a standard detachable cable. This facilitates end user cable replacement.
Figure 2-10 illustrates the keyed connector protocol.
Series A Connectors
Series B Connectors
◆Series A plugs are
always oriented upstream
towards the Host System
A Plugs
(From the
USB Device)
A Receptacles
(Downstream Output
from the USB Host orHub)
◆Series B plugs are
always oriented downstream towards
the USB Device
B Plugs
(From the
Host System)
B Receptacles
(Upstream Input to the
USB Device or Hub)
Figure 3-10 Keyed Connector Protocol
The following list explains how the plugs and receptacles can be mated:
• Series “A” receptacle mates with a Series “A” plug. Electrically, Series “A” receptacles function as outputs
from host systems and/or hubs.
• Series “A” plug mates with a Series “A” receptacle. The Series “A” plug always is oriented towards the host
system.
• Series “B” receptacle mates with a Series “B” plug (male). Electrically, Series “B” receptacles function as
inputs to hubs or devices.
• Series “B” plug mates with a Series “B” receptacle. The Series “B” plug is always oriented towards the USB
hub or device.