Freescale Semiconductor MPC8313E PowerQUICC II Pro Family Reference Manual page 787

Table 15-41 describes the fields of the MACCFG2 register.
Bits Name
0–15 — Reserved
16–19 Preamble This field determines the length in bytes of the preamble field preceding each Ethernet start-of-frame
Length delimiter byte. Values from 0x3 to 0xF are supported by the controller. The default value of 0x7 should
not be altered in order to guarantee reliable operation with IEEE 802.3 compliant hardware.
20–21 — Reserved
22–23 I/F Mode This field determines the type of interface to which the MAC is connected. Its default is 00.
00 Reserved bit mode (not supported) (10 Mbps GENDEC/GPSI)
01 Nibble mode (MII) (10/100 Mbps MII/RMII)
10 Byte mode () (1000 Mbps). Reserved if neither GMII or TBI are supported.
11 Reserved
24 PreAM RxEN User defined preamble enable for received frames. This bit is cleared by default.
0 The MAC skips the Ethernet preamble without returning it.
1 The MAC recovers the received Ethernet preamble and passes it to the driver at the start of each
25 PreAM TxEN User defined preamble enable for transmitted frames. This bit is cleared by default.
0 The MAC generates a standard Ethernet preamble.
1 If a user-defined preamble has been passed to the MAC it is transmitted instead of the standard
26 Huge Huge frame enable. This bit is cleared by default.
Frame 0 Limit the length of frames received to less than or equal to the maximum frame length value
1 Frames are transmitted and received regardless of their relationship to the maximum frame length.
Note that if Huge Frame is cleared, the user must ensure that adequate buffer space is allocated for
27 Length Length check. This bit is cleared by default.
check 0 No length field checking is performed.
1 The MAC checks the frame's length field on receive to ensure it matches the actual data field length.
MPC8313E PowerQUICC™ II Pro Integrated Processor Family Reference Manual, Rev. 2
Freescale Semiconductor
Table 15-41. MACCFG2 Field Descriptions
received frame. If the preamble is less than 7 bytes, 0's are prepended to pad it to 7 bytes. Not
applicable to or RMII 10/100 modes.
preamble. Otherwise the standard Ethernet preamble is generated. The Preamble Length field
should be left at its default setting if a user-defined preamble is transmitted. Not applicable to or
RMII 10/100 modes.
(MAXFRM[Maximum Frame]) and limit the length of frames transmitted to less than the maximum
frame length.
See Section 15.6.7, "Buffer
Frame type
Receive or transmit > maximum frame length
Receive = maximum frame length
Transmit = maximum frame length
Receive or transmit < maximum frame length
received frames. See Section 15.5.3.5.5, "Maximum Frame Length Register
information.
Transmitted frames are not checked.
Description
Descriptors," for further details of buffer descriptor bit updating.
Frame length
Enhanced Three-Speed Ethernet Controllers
Packet Buffer descriptor
truncation updated
yes yes
no yes
no no
no no
(MAXFRM)," for further
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