Section 20 Ethernet Controller (EtherC)
Rev. 1.00 Mar. 12, 2008 Page 786 of 1178
REJ09B0403-0100
20.4.6
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
bus.
[1]
[2]
[3]
[4]
[1]
[2]
[3]
[4]
[5]
......
......
Case A
(short IPG)
Case B
(long IPG)
Figure 20.12 Changing IPG and Transmission Efficiency
20.4.7 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:
(1) 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
register (FCFTR) of the E-DMAC. The TIME parameter included in the PAUSE frame at this
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
Содержание H8S Family
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Страница 838: ...Section 20 Ethernet Controller EtherC Rev 1 00 Mar 12 2008 Page 790 of 1178 REJ09B0403 0100...
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