Answer:
The 630xx/631xx has two eight-byte buffers, one for the control endpoint and one for data endpoint. The USB Specification requires that a device has at least 1 IN endpoint. Therefore, the data enpoint must be configured as an IN endpoint. The only mechanism to send data OUT to the device is to use SET_REPORT over the control endpoint. To learn more about SET_REPORT, please refer to the USB Specification.