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USB MultiSwitch
TM
Hub
Datasheet
Revision 1.91 (08-22-07) 42 SMSC USB2524
DATASHEET
A Block Read differs from a block write in that the repeated start condition exists to satisfy the I
2
C
specification's requirement for a change in the transfer direction.
Figure 7.2 SMBus Block Read
7.3.2 Invalid Protocol Response Behavior
Registers that are accessed with an invalid protocol are not updated. A register is only updated
following a valid protocol. The only valid protocols are Write Block and Read Block, which are
described above.
The Hub only responds to the hardware selected Slave Address. Attempting to communicate with the
Hub over SMBus with an invalid slave address or invalid protocol results in no response, and the
SMBus Slave Interface returns to the idle state. The only valid registers that are accessible by the
SMBus slave address are the registers defined in the Registers Section. See Undefined Registers for
the response to undefined registers.
7.3.3 General Call Address Response
The Hub does not respond to a general call address of 0000_000b.
7.3.4 Slave Device Time-Out
According to the SMBus Specification, V1.0 devices in a transfer can abort the transfer in progress
and release the bus when any single clock low interval exceeds 25ms (T
TIMEOUT, MIN
). Devices that
have detected this condition must reset their communication and be able to receive a new START
condition no later than 35ms (T
TIMEOUT, MAX
).
Note: Some simple devices do not contain a clock low drive circuit; this simple kind of device typically
resets its communications port after a start or stop condition. The Slave Device Time-Out must
be implemented.
7.3.5 Stretching the SCLK Signal
The Hub supports stretching of the SCLK by other devices on the SMBus. The Hub does not stretch
the SCLK.
7.3.6 SMBus Timing
The SMBus Slave Interface complies with the SMBus AC Timing Specification. See the SMBus timing
in the “Timing Diagram” section.
Block Read
1
SS Slave Address Register AddressWr A
17118
A
1
Slave Address Rd A
711
81 1 188
P
181
A AAA
Byte Count = N
Data byte 1 Data byte 2 Data byte N
...