USB2512AI datasheet(43/63 Pages) MICROCHIP

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USB 2.0 Hi-Speed Hub Controller

Datasheet

SMSC USB251xB/xBi

Revision 2.2 (02-17-12)

DATASHEET

5.3.2.1

Block Write/Read

The block write begins with a slave address and a write condition. After the command code, the host

issues a byte count which describes how many more bytes will follow in the message. If a slave had

20 bytes to send, the first byte would be the number 20 (14h), followed by the 20 bytes of data. The

byte count may not be zero. A block write or read allows a transfer maximum of 32 data bytes.

Note:

For the following SMBus tables:

Figure 5.1 Block Write

5.3.2.2

Block Read

A block read differs from a block write in that the repeated start condition exists to satisfy the I2C

specification’s requirement for a change in the transfer direction.

Figure 5.2 Block Read

5.3.2.3

Invalid Protocol Response Behavior

Note that any attempt to update registers with an invalid protocol will not be updated. The only valid

protocols are write block and read block (described above), where the hub only responds to the 7-bit

hardware selected slave address (0101100b). Also, the only valid registers for the hub are outlined in

Section 5.1 on page 27. Attempts to access any other registers will return no response.

5.3.3

Slave Device Timeout

Devices in a transfer can abort the transfer in progress and release the bus when any single clock low

interval exceeds 25 ms (TTIMEOUT, MIN). The master must detect this condition and generate a stop

condition within or after the transfer of the interrupted data byte. Slave devices must reset their

communication and be able to receive a new START condition no later than 35 ms (TTIMEOUT, 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 timeout must

be implemented.

Denotes Master-to-Slave

Denotes Slave-to-Master

Slave Address

171

...

Byte Count = N

Data byte 1

Data byte 2

Data byte N

Slave Address

...

Byte Count = N

Data byte 2

Data byte 1

Data byte N

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