28.3.2.6.4 Auto Zero Length Packet

Some device classes require a generation of a zero-length packet to signal the end of a transfer. If the transferred data are an exact multiple of the packet size for the specific endpoint, a ZLP is appended to signal the end of the transfer. Enable the auto zero length packet (AZLP) function to perform this generation automatically, thus removing the need for application software or CPU intervention to perform this task.

For IN Endpoints, the device will send a ZLP to the host after CNT bytes have been sent if CNT is a multiple of the maximum payload size. For OUT Endpoints, the device will respond with ACK to a ZLP if MCNT bytes are received while responding with NAK to any other data packet.