Operation By Ipg Setting - Renesas H8S Family Hardware Manual

Section 20 Ethernet Controller (EtherC)

Operation by IPG Setting

The EtherC supports the function to change the Inter Packet Gap (IPG ), the non-transmission

period between transmit frames. By changing the set values of the IPG setting register (IPGR), the

transmission efficiency can be raised and lowered from the standard value. IPG settings are

prescribed in IEEE802.3 standards. When changing settings, adequately check that the respective

devices can operate smoothly on the same network.

Note: IPG may be longer than the set value, depending on the state of the circuit and the system

Figure 20.12 Changing IPG and Transmission Efficiency

Flow Control

The EtherC supports flow control functions conforming to IEEE802.3x in full-duplex operations.

Flow control can be applied to both receive and transmit operations. The methods for transmitting

PAUSE frames when controlling flow are as follows:

Automatic PAUSE Frame Transmission

For receive frames, PAUSE frames are automatically transmitted when the number of data in the

receive FIFO (included in E-DMAC) reaches the value set in the flow control FIFO threshold

time is set by the automatic PAUSE frame setting register (APR). The automatic PAUSE frame

transmission is repeated until the number of data in the receive FIFO becomes less than the

FCFTR setting as the receive data is read from the FIFO.

The upper limit of the number of retransmissions of the PAUSE frame can also be set by the

automatic PAUSE frame retransmission count set register (TPAUSER). In this case, PAUSE

frame transmission is repeated until the number of data becomes FCFTR value set or below, or the

Rev. 1.00 Mar. 12, 2008 Page 786 of 1178

REJ09B0403-0100