Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 772

SCC Ethernet Mode
Bits Name
6 PRO Promiscuous
0 Check the destination address of incoming frames.
1 Receive the frame regardless of its address.
7 BRO Broadcast address
0 Receive all frames containing the broadcast address.
1 Reject all frames containing the broadcast address, unless PRO = 1.
8 SBT Stop backoff timer
0 The backoff timer is functioning normally.
1 The backoff timer for the random wait after a collision is stopped when carrier sense is active.
Retransmission is less aggressive than the maximum allowed in IEEE 802.3. The persistence
(P_PER) feature in the parameter RAM can be used in combination with or in place of SBT.
9 LPB Loopback operation
0 Normal operation
1 External loopback is used if GSMR[DIAG] is set for normal operation; internal loopback is used
if DIAG is configured for loopback operation.
10 SIP Sample input pins
0 Normal operation
1 After a frame is received, the value on PB(16–23) is sampled and written to the end of the last
buffer of the frame. This value is called a tag byte. If the frame is discarded, the tag byte is also
discarded.
11 LCW Late collision window
0 A late collision is any collision that occurs at least 64 bytes from the preamble.
1 A late collision is any collision that occurs at least 56 bytes from the preamble.
12–14 NIB Number of ignored bits. Determines how soon after RENA assertion the ethernet controller should
begin looking for the start frame delimiter. Typically NIB = 101 (22 bits).
000 Begin searching 13 bits after the assertion of RENA.
001 Begin searching 14 bits after the assertion of RENA.
...
111 Begin searching 24 bits after the assertion of RENA.
15 FDE Full duplex ethernet
0 Disable full-duplex ethernet mode
1 Enable full-duplex ethernet mode
Note: When FDE = 1, PSMR[LPB] must be set also.
27.18 SCC Ethernet Receive Buffer Descriptor
The ethernet controller uses the RxBD to report on the received data for each buffer.
0 1
Offset + 0 E —
Offset + 2
Offset + 4
Offset + 6
27-16
Table 27-7. PSMR Field Descriptions (continued)
2 3 4 5 6
W I L F —
Rx Data Buffer Pointer
Figure 27-6. SCC Ethernet RxBD
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
7 8 9 10 11
M — LG NO
Data Length
12 13 14 15
SH CR OV CL
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