Bixolon SRP-350 User Manual

 

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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 plugs are 

always oriented upstream 

towards the Host System 

A Plugs 

(From the 

)

A Receptacles   

(Downstream Output 

) 

 

◆

Series B plugs are 

always oriented downstream towards 

the USB Device 

B Plugs 

(From the 

) 

 
 
B Receptacles 

(Upstream Input to the 

) 

 

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.