Information

Enhanced Three-Speed Ethernet Controllers
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 16-129
• The first TxBD of every frame containing a custom preamble has its PRE bit set
• An 8-byte custom preamble sequence appears before the Ethernet DA field in the first transmit data
buffer
The definition of the 8-byte custom preamble sequence is shown in Figure 16-119.
The fields of the custom preamble sequence are described in Table 16-128. It should be noted that use of
preamble octets matching the standard start of frame delimiter (0xD5) can be expected to trigger premature
frame reception by the receiving station.
16.6.2.5.2 User-Visible Preamble Reception
To return the received preamble, the user must ensure that:
• MACCFG2[PreAm RxEN] bit is set
• Space for an 8-byte preamble sequence is allowed before the Ethernet DA field in the first receive
data buffer of each frame
The definition of the 8-byte received preamble sequence is shown in Figure 16-120.
Byte Offsets
0123456789101112131415
0–1 PreOct0 PreOct1
2–3 PreOct2 PreOct3
4–5 PreOct4 PreOct5
6–7 PreOct6
Figure 16-119. Definition of Custom Preamble Sequence
Table 16-128. Custom Preamble Field Descriptions
Bytes Bits Name Description
0–1 0–7 PreOct0 Octet #0 of custom transmit preamble. This is the first octet of preamble sent.
8–15 PreOct1 Octet #1 of custom transmit preamble. This is the second octet of preamble sent.
2–3 0–7 PreOct2 Octet #2 of custom transmit preamble. This is the third octet of preamble sent.
8–15 PreOct3 Octet #3 of custom transmit preamble. This is the fourth octet of preamble sent.
4–5 0–7 PreOct4 Octet #4 of custom transmit preamble. This is the fifth octet of preamble sent.
8–15 PreOct5 Octet #5 of custom transmit preamble. This is the sixth octet of preamble sent.
6–7 0–7 PreOct6 Octet #6 of custom transmit preamble. This is the seventh octet of preamble sent. The last octet
(the start of frame delimiter) is generated by the MAC automatically.
8–15 — Reserved; should be cleared.
Byte Offsets
0123456789101112131415
0–1 PreOct0 PreOct1
2–3 PreOct2 PreOct3
4–5 PreOct4 PreOct5
6–7 PreOct6
Figure 16-120. Definition of Received Preamble Sequence