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Seiko Epson Corporation
S2R72A21 Application Note
(Rev.1.00)
1: S2R72A21 would detect the SE0 condition and transit to FS_LS state
Since the periodic SOF sent from the Portable Device (as Host) is lost, the SE0 would be detected by EXT
port’s Bus state. When the S2R72A21 detects the SE0 condition for 3ms by the Bus state, the HS
Synchronizer’s operation would stop and the FS_LS state transition is done where the Bus Switch path
between INT-EXT gets “ON”.
Here, the Host (Portable Device) is lost and the Device (Host SoC) is left on the Bus. In this situation the
bus would deviate from the USB specification and the S2R72A21 may not follow the Bus state.
Furthermore, the bus state on the EXT port may be unstable depending on the contact situation of the
connector during detach, since the Portable Device is detached while packets are exchanged. This may
provoke malfunction of the S2R72A21.
2: Host SoC would judge HS disconnection by Bus invalid condition.
From the Bus Switch path connection, the Host SoC will judge the disconnection of the Portable Device
by detecting the EXT port’s Bus invalid condition for a certain period of time.
3: Notification of HS disconnection from the Host SoC to S2R72A21
Notification from the Host SoC to S2R72A21 of the disconnection detection is done by ENABLE=0.
This initializes the state which deviated from the USB specification, and fixes the malfunction caused by
the unstable contact situation of the connector during detach.
In all cases above, re-attach of the Portable Devices are accepted after recovering to ENABLE=1 (ENABLE=1:
the Bus Switch Path would return to the initial condition where the INT port and the EXT port are connected).
