Using the USB20H04 with an On-The-Go Host

SMSC AN 10.4

Page 4

Rev. 04-07-03

APPLICATION NOTE

Protocol Definition

Before attempting either of these two methods, the USB20H04 must determine that the following two initial

conditions have been met:

DP/DM lines on OTG Host idle (SE0) for 2ms

Once the initial conditions have been satisfied, both pulsing methods will be tried by the hub. First, the data-line

required to support one method, while the B-device is required to support both methods.

Data Line Pulsing: USB20H04 turns on its data line pull-up resistor (either DP or DM) for a period of 5 ms

to 10 ms. If the OTG-Host is designed to support the data-line pulsing method of SRP, it will detect that a

data line (either DP or DM) has gone high and generate an indication that SRP has been detected. This

2.1V when connected to an OTG Host. Because the maximum allowed capacitance on a dual-role OTG

device is 6.5uF, the line will be driven to at least 2.1V. This pulse will wake up the sleeping OTG Host.

However, if the USB20H04 is connected to a standard host, the capacitance will be greater than 96uF;

therefore the line will never exceed 2.0V and will not be detected by standard host. This technique has

been designed to avoid damage to a standard USB host.

After the OTG Host detects one of the above pulsing methods, it will reset the entire USB tree, and will re-

enumerate each device.

After completion of enumeration, the downstream device will be capable of

communicating through Hub, to the Host.