Table 19-1. Fcs/Sa Enable - Possible Configurations; Table 19-2. Fcs/Pad Enable - Possible Configurations; Table 19-3. Fcsnlan Tag Enable - Possible Configurations - IBM PowerPC 405GP User Manual

• Source address replacement. When chosen, EMAC replaces the source address received from the
Transmit FIFO with the content of the Individual Address High and Individual Address Low
registers. This mode is mutually exclusive with the source address insertion mode.
• Add four FCS bytes. EMAC calculates the FCS for the transmitted packet. The FCS is appended to
data coming from the Transmit FIFO or padding bytes (if added).
• VLAN Tag insertion. When chosen, EMAC adds the content of the VLAN Tag field to the
transmitted packet (see "VLAN Support" on page 19-18). EMAC uses the content of the VLAN
TPID and VLAN TCI registers for the VLAN Tag value. This feature is supported only when the
packet coming from the Transmit FIFO does not contain an FCS. This mode is mutually exclusive
with the VLAN Tag replacement mode.
• VLAN Tag replacement. When chosen, EMAC replaces the content of the VLAN Tag field in the
transmitted packet. EMAC uses the content of the VLAN TPID and VLAN TCI registers for the
VLAN Tag value. This feature is supported only when the packet coming from the Transmit FIFO
does not contain an FCS. This mode is mutually exclusive with the VLAN Tag insertion mode.
Table 19-1 summarizes the possible options of adding FCS and source address to the transmitted
packet.
Table 19·1. FCS/SA Enable· Possible Configurations
Configuration Options
EMAC Action
Generate FCS
Insert SA
Replace SA Add FCS
Add SA Replace SA
0 Don't care Don't care N N N
1 0 0
y
N N
1
0 1 Y N
y
1 1 0
Y
y
N
Table 19-2 summarizes the possible options of adding FCS and padding to the transmitted packet.
Table 19·2. FCS/Pad Enable· Possible Configurations
Configuration Options
EMAC Action
Generate FCS Generate Pad Adc;l FCS
Add Pad
0 Don't care N
N
1 0
y
N
1 1 Y
y
Table 19-3 summarizes the possible options of adding FCS and VLAN Tag to the transmitted packet.
Table 19·3. FCSNLAN Tag Enable· Possible Configurations
Configuration Options EMAC Action
Insert VLAN Replace VLAN Insert VLAN Replace VLAN
Generate FCS Tag Tag Add FCS Tag Tag
0
Don't care Don't care
N
N N
1 0 0
y
N N"
1 0 1 Y N
y
Preliminary Ethernet Media Access Controller
19-11