MPC8280 datasheet(796/1386 Pages) FREESCALE

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SCC Ethernet Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

25-8

Freescale Semiconductor

0x4C

MINFLR

Hword Minimum frame length register. The Ethernet controller checks the incoming

frame’s length against MINFLR (typically 64 decimal). If the received frame is

smaller than MINFLR, it is discarded unless PSMR[RSH] is set, in which case,

SH is set in the last BD for the frame. For transmitting a frame that is too short,

the Ethernet controller pads the frame to make it MINFLR bytes long, depending

on how PAD is set in the TxBD and on the PAD value in the parameter RAM.

0x4E

MAXD1

Hword Max DMA

n length register. Gives the option to stop system bus writes after a

frame exceeds a certain size. However, this value is valid only if an address

match is found. The Ethernet controller checks the length of an incoming Ethernet

frame against this user-defined value (usually 1520 decimal). If this limit is

exceeded, the rest of the incoming frame is discarded. The Ethernet controller

waits until the end of the frame or until MFLR bytes are received and reports the

frame status and the frame length in the last RxBD.

MAXD1 is used when an address matches an individual or group address.

MAXD2 is used in promiscuous mode when no address match is detected. In a

monitor station, MAXD2 can be much less than MAXD1 to receive entire frames

addressed to this station, but only the headers of the other frames are received.

0x50

MAXD2

Hword

0x52

MAXD

Hword Rx max DMA.

0x54

DMA_CNT

Hword Rx DMA counter. A temporary down-counter used to track frame length.

0x56

MAX_B

Hword Maximum BD byte count.

0x58

GADDR1

Hword Group address filter 1–4. Used in the hash table function of the group addressing

mode. 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.

0x5A

GADDR2

0x5C

GADDR3

0x5E

GADDR4

0x60

TBUF0_DATA0

Word

Save area 0—current frame.

0x64

TBUF0_DATA1

Word

Save area 1—current frame.

0x68

TBUF0_RBA0

Word

0x6C

TBUF0_CRC

Word

0x70

TBUF0_BCNT

Hword

0x72

PADDR1_H

Hword The 48-bit individual address of this station into this location. PADDR1_L is the

lowest order hword and PADDR1_H is the highest order hword.

0x74

PADDR1_M

0x76

PADDR1_L

0x78

P_PER

Hword Persistence. Lets the Ethernet controller be less aggressive after a collision.

Normally, 0x0000. It can be a value between 1 and 9 (1 is most aggressive). The

value is added to the retry count in the backoff algorithm to reduce the chance of

transmission on the next time slot.

Note: Using P_PER is fully allowed in the Ethernet/802.3 specifications. A less

aggressive backoff algorithm used by multiple stations on a congested Ethernet

LAN increases overall throughput by reducing the chance of collision.

PSMR[SBT] offers another way to reduce the aggressiveness of the Ethernet

controller.

0x7A

RFBD_PTR

Hword Rx first BD pointer.

Table 25-1. SCC Ethernet Parameter RAM Memory Map (continued)

Offset 1

Name

Width

Description

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