MPC8280 datasheet(1243/1386 Pages) FREESCALE

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Fast Ethernet Controller

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

36-9

Table 36-2. Ethernet-Specific Parameter RAM

Offset1

Name

Width

Description

0x3C

STAT_BUF

Word

Buffer of internal usage

0x40

CAM_PTR

Word

CAM address. For FCC Fast Ethernet operation the CAM should be located on the

same bus as the data buffers.

0x44

C_MASK

Word

Constant MASK for CRC (initialize to 0xDEBB_20E3). For the 32-bit CRC-CCITT.

0x48

C_PRES

Word

Preset CRC (initialize to 0xFFFF_FFFF). For the 32-bit CRC-CCITT.

0x4C

CRCEC2

Word

CRC error counter. Counts each received frame with a CRC error. Does not count

frames not addressed to the station, frames received in the out-of-buffers condition,

frames with overrun errors, or frames with alignment errors.

0x50

ALEC 2

Word

Alignment error counter. Counts frames received with dribbling bits. Does not count

frames not addressed to the station, frames received in the out-of-buffers condition, or

frames with overrun errors.

0x54

DISFC 2

Word

Discard frame counter. Incremented for discarded frames because of an out-of-buffers

condition or overrun error. The CRC need not be correct for this counter to be

incremented.

0x58

RET_LIM

Hword Retry limit (typically 15 decimal). Number of retries that should be made to send a

frame. If the frame is not sent after this limit is reached, an interrupt can be generated.

0x5A

RET_CNT

Hword Retry limit counter. Temporary decrementer used to count retries made.

0x5C

P_PER

Hword Persistence. Allows the Ethernet controller to be less persistent after a collision.

Normally cleared, P_PER can be from 0 to 9 (9 = least persistent). The value is added

to the retry count in the backoff algorithm to reduce the chance of transmission on the

next time-slot. Using a less persistent backoff algorithm increases throughput in a

congested Ethernet LAN by reducing the chance of collisions. FPSMR[SBT] can also

reduce persistence of the Ethernet controller. The Ethernet/802.3 specifications

permit the use of P_PER.

0x5E

BOFF_CNT

Hword Backoff counter

0x60

GADDR_H

Word

Group address filters high and low are used in the hash table function of the group

addressing mode. The user may write zeros to these values after reset and before the

Ethernet channel is enabled to disable all group hash address recognition functions.

The SET GROUP ADDRESS command is used to enable the hash table. See

Section 36.13, “Hash Table Algorithm.”

0x64

GADDR_L

Word

0x68

TFCSTAT

Hword Out-of-sequence TxBD. Includes the status/control, data length, and buffer pointer

fields in the same format as a regular TxBD. Useful for sending flow control frames.

This area’s TxBD[R] is always checked between frames, regardless of FPSMR

x[FCE].

If it is not ready, a regular frame is sent. The user must set TxBD[L] when preparing

this BD. If TxBD[I] is set, a TXC event is generated after frame transmission. This area

should be cleared when not in use.

0x6A

TFCLEN

Hword

0x6C

TFCPTR

Word

0x70

MFLR

Hword Maximum frame length register (typically1518 decimal). If the Ethernet controller

detects an incoming frame exceeding MFLR, it sets RxBD[LG] (frame too long) in the

last RxBD, but does not discard the rest of the frame. The controller also reports the

frame status and length of the received frame in the last RxBD. MFLR includes all

in-frame bytes between the start frame delimiter and the end of the frame.

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