Standard USB/mini-USB interface and OTG

Source: Internet
Author: User


Http://blog.csdn.net/zhandoushi1982/archive/2010/08/16/5814741.aspx

(1) USB

(2) mini USB

USB devices include host, OTG, and device. The ID foot is used only in the OTG function.

A. If your system only uses slave, use the B interface. Slave is implemented whenever it is suspended.

If it is an OTG device, its system controller will determine the level of the ID foot of an external device and decide what kind of device is inserted:

B. If it is a high-level device, the B-connector is inserted. In this case, the OTG device adopts the master mode );

C. If the ID is low, the interface is inserted. Then the OTG device uses the HNP dialogue protocol to determine which node is the master and slave with the peripherals.

D, there is also an active OTG settings, that is, after accessing the peripherals, click the host in the OTG device to enable, will force the ID to be lowered. At this time, the relationship between the master and slave is determined.
Generally, we use B-type mini-USB ports on our mobile phones.
(3) Summary

From left to right: miniusb public port (a plug), miniusb public port (B plug), USB public port (B), USB mother port (a socket) USB public port (A-type plug ).

(4) OTG

Features: It can act as both a host and a device, that is, DRD (dual-role-devices). The OTG device can still be connected to a PC and used as a general peripherals, that is, POD (peripheral-only device ). Protocol Description: two new protocols, Session Request protocol and host negotiation protocol, are introduced in usb otg.

 

(5) SRP

 

SRP is used by Device B to request a to establish a session and use the bus. The a device in the OTG system is generally powered by a battery. Therefore, the power management of the OTG system is very important. To reduce the power consumption of the OTG system, OTG requires that a can turn off the power of vbus when there is no bus activity. In this way, after a device B is connected to device A, it initializes the SRP and sends it to device A, requesting that device a provide current support on vbus for communication. In OTG, a session is defined as the time when a type A device effectively powers the power bus vbus. DRD can be either A or B. Therefore, DRD must support SRP initialization and response SRP. Pod can only be B, so only SRP can be initialized.

 

(6) HNP

 

HNP is used for role switching when two OTG devices are connected. When two DRDs are connected, which device acts as the host and why is it used as the host? To solve these two problems, a new protocol-host negotiation protocol (HNP) was proposed in OTG ). A new interface-mini-AB connector tacle and Mi-ni-A plug-is also defined in OTG) and mini-B plug ). One pin-ID pin is added to the micro AB outlet, micro a plug, and Micro B plug. To achieve HNP, in short, when two OTG devices are connected, master/Slave status can be negotiated through the HNP protocol. The negotiation process is as follows:

In the miniature a plug, the ID pin is grounded, and in the miniature B plug, the ID pin is suspended. In OTG, if the device's ID pin is grounded (the device on the right), the device is a host by default; otherwise, the device is a peripheral. In addition, the host and peripheral functions can be exchanged through host negotiation protocol during device connection and usage. For example, assume that B-device on the left of Figure 1 is a handheld PDA and A-device on the right is a printer. The printer is initialized as a host due to the connection line. However, the driver of the printer exists in the PDA. In this case, the PDA is used as the host and the printer is used as the peripherals. HNP can be used to conveniently implement this function, without removing the need to unplug the connection line to change the direction of the plug, re-connect the printer and PDA.

 

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