USB-TO-GPIO datasheet(40/50 Pages) TI1

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B.4

Packet Error Checking (PEC) Implementation

B.5

Communication Clock Speed and Clock Stretching

B.6

Configuration of Pullup Resistors for ALERT, DATA, and CLOCK Lines

B.7

Limitations

Packet Error Checking (PEC) Implementation

By default, the USB Interface Adapter firmware implements PEC for all the different commands. However,

the implementation of PEC byte is optional. There is a special host PC to USB Interface Adapter

command that can be used to turn PEC on or off (see Section B.23).

If PEC is on or enabled, the firmware in the USB Interface Adapter either appends a PEC byte to a

command sent to one or multiple slave devices or checks the validity of a PEC byte received from a slave

device.

The default clock speed is 100 kHz, which is compatible with PMBUS 1.0 and SMBUS 2.0. For

compatibility with future PMBUS specs, the clock speed can be increased to 400 kHz (see Section 3.9).

For each PMBUS/SMBUS transaction, the accumulative time of clock stretching cannot be more 25 ms.

Refer to Section 3.8 for more details on this topic.

Because of the limited capabilities of the TUSB3210 USB peripheral chip, the USB Interface Adapter has

the following limitations:

• Extended Command is not supported. Only the first 256 commands are supported.

• For any block write or block read command, the number of data bytes is limited to 32 bytes only, even

though the PMBUS specs support up to 256 bytes of data per transaction.

• Address Resolution Protocol (ARP) is not supported, so no multiple masters are allowed.

• Host Notify Protocol is not supported (see Section B.3).

PMBUS/SMBUS Communications

SLLU093 – August 2006

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USB-TO-GPIO Datasheet(PDF) 40 Page - Texas Instruments