Bus-powered Operation in Backward-compatability (68300A) Mode

Question: What are the possible solutions in Bus-powered Operation in Backward-compatability (68300A) Mode?



The 68300B does not support operation with a bMaxpower value greater than 0x01 in backward-compatability (68300A) mode. The 68300A did not support bus-powered operation, so the 68300B's backward-compatability mode was not intended for use in bus-powered designs. While the bmAttribute fields can be set to report bus-powered operation (0x80), the bMaxpower fields can only be set to 0x00 or 0x01 in 68300A mode. Three solutions are possible:

1) Set the bmAttributes fields to 0x80 and bMaxPower to 0x01. The device will report as bus-powered, but will only request 2mA of power from the host. This may result in USB certification failure if the device draws more than 2mA of power from USB.

2) Use 68300B pinout. The bus-powered operation with 68300B mode is completely functional (when used in conjunction with the DRVPWRVLD feature) and allows for full control over the bMaxPower values. Please refer to the AT2LP datasheet for more information about 68300B mode operations.

3) Use FX2LP and CY4611B firmware that has been modified to support the 68300A pinout with bus-powered support. Please refer to the CY4611B documentation for more details.