NEC Network Controller uPD98502 - Manual (Page 303)

CHAPTER 5 ETHERNET CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 303
Short frames are automatically padded by the transmit logic if PADEN bit in En_MACC1 register is set. If the
transmit frame length exceeds 1518 bytes, Ethernet Controller will assert an interrupt. However, the entire frame will
be transmitted (no truncation).
If the current descriptor does not contain the end of frame, Ethernet Controller reads next buffer descriptor, and
then reads the continuous data from the data buffer. After Ethernet Controller sent out the whole packet,. Ethernet
Controller writes the transmission status into the last descriptor (L=1), and generates an interrupt to indicates the end
of transmission. After this, Ethernet Controller fetches the next Transmit Buffer Descriptor, and then if the next data is
available, it will be sent out in the same manner.
When Ethernet Controller received the pause control frame and if it is active, Ethernet Controller transmitter stops
immediately if no transmission is in progress or continues transmission until the current frame either finishes or
terminates with a collision. When the pause timer was expired or Ethernet Controller received a zero value of pause
control frame, Ethernet Controller resumes transmission with the next frame.
Transmit procedure is as follows: (Figure 5-7)