If the MAC core is configured to have the FCS field passed in by you, the transmission timing is as depicted in the following figure. In this case, it is your responsibility to ensure that the frame meets the Ethernet minimum frame length requirements. If frame length requirements are not met, the core appends zeros at the end of the supplied frame to meet the minimum frame length. Although this does not cause the Transmit Statistics Vector to indicate a bad frame, it results in an errored frame as received by the link partner MAC (due to the detection of an FCS error).
Figure 1. Frame Transmission with User-Supplied FCS
