SH7710 Datasheet, PDF (765/996 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 18 Ethernet Controller (EtherC)
18.4.8 Operation by IPG Setting
The EtherC has a function to change the non-transmission period IPG (Inter Packet Gap) 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.
Case A
(short IPG)
[1]
[2]
[3]
[4]
[5]
......
Packet IPG*
Case B
(long IPG)
[1]
[2]
[3]
[4]
......
Note: * IPG may be longer than the set value, depending on the state of the line and the system bus.
Figure 18.10 Changing IPG and Transmission Efficiency
18.4.9 Direction for IEEE802.1Q Qtag
The EtherC supports IEEE802.1Q frame processing. It can add or delete Qtags to or from frames
processed in relay. This function can also transmit and receive QoS frames. During relaying, if the
Ethernet device connected to one MAC controller cannot transmit or receive QoS frames, it can be
converted to the normal IEEE802.3 frames and relayed in this LSI. Whether to add or delete Qtags
is determined by the added Qtag value set register (TSU_ADQT0/1). Figure 18.11 shows an
outline of the Qtag add function while figure 18.12 shows the comparison between the normal
Ethernet frames and IEEE802.1Q frames (with Qtag). For details on setting Qtag, refer to the
specifications on Qtag control specified in IEEE802.1Q.
Rev. 2.00 Dec. 07, 2005 Page 723 of 950
REJ09B0079-0200