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Seiko Epson Corporation
S2R72A21 Application Note
(Rev.1.00)
5. Operation within each connection example
Within the 3 system connection examples indicated on Chapter 4, we would explain each of the operation such as
the ADJ setting, BC control, Role Switch control and the disconnection detection control separately within
section 5.1-5.3. Table 5.1 is the summary of the connection, function, pin setting, disconnection detection control
for each system structure.
Role Switch is a function to switch the Host & Device role as indicated on Chapter 2, and some Portable Devices
have this function. S2R72A21 is a Re-Synchronization IC which also follows the Role Switch function.
In case where the Portable Device has the Role Switch function, there would be a negotiation to switch the role of
the Host and the Device after FS to HS connection (corresponding to the USB specification). After that the
Portable Device would play as a Host and issue the Bus reset and resume the HS communication again via FS to
HS connection.
As mentioned on the S2R72A21 Data sheet (section 6.1.1), S2R72A21 would transit from HS state to FS_LS
state automatically when over 3ms of SE0 is detected and the Bus Switch connection between INT-EXT would
be valid. In other words, within the above Role switch operation sequence, S2R72A21 would detect over 3ms of
SE0, automatically validate the Bus Switch in between INT-EXT for FS communication, and transit to HS
communication connection condition after Role Switch.
Table 5.1
Summary of each system structure
Section
USB port connection
Function
Pin
Disconnection
detection
control after
Role Switch
INT
EXT
I2C IF
HS transmission
current control
ADJ
4.1
5.1
Host SoC
(BC)
PD
Usable
INT/EXT
Fine adjustment
I2C
address
ENABLE pin
control; 0 to 1
4.2
5.2
Host SoC
(BC)
PD
Unusable
EXT only
Rough tuning
HS
transmissi
on current
control
VBUS supply:
Stop to resume
4.3
5.3
PD
Host SoC
(BC)
Unusable
EXT only
Rough tuning
HS
transmissi
on current
control
VBUS supply:
Stop to resume
BC = BC Regulator
PD = Portable Device
Содержание S2R72A21
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