DP83821 datasheet(50/86 Pages) NSC

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4.0 Register Set (Continued)

4.2.11 Reserved

This register is reserved. It must always be read and written as 00000000h.

4.2.12 Transmit Configuration Register

This register defines the Transmit Configuration for DP83821. It controls such functions as Loopback, Heartbeat, Auto

Transmit Padding, programmable Interframe Gap, Fill & Drain Thresholds, and maximum DMA burst size.

Tag: TXCFG

Size: 32 bits

Hard Reset: 00000120

Offset: 0028h

Access: Read Write

Soft Reset: 00000120

bit

tag

description

usage

CSI

Carrier Sense Ignore

Setting this bit to 1 causes the transmitter to ignore carrier sense activity,

which inhibits reporting of CRS status to the transmit status register, and

inhibits logging of TXCSErrors in the MIB counter block. When this bit is 0

(default), the transmitter will monitor the CRS signal during transmission

and reflect valid status in the transmit status register and MIB counter

block. This bit must be set to enable full-duplex operation.

HBI

HeartBeat Ignore

Setting this bit to 1 causes the transmitter to ignore the heartbeat (CD)

pulse which follows the packet transmission and inhibits logging of

TXSQEErrors in the MIB counter block. When this bit is set to 0 (default),

the transmitter will monitor the heartbeat pulse and log TXSQEErrors to the

MIB counter block. This bit must be set to enable full-duplex operation

MLB

MAC Loopback

Setting this bit to a 1 places the DP83821 MAC into a loopback state which

routes all transmit traffic to the receiver, and disables the transmit and

receive interfaces of the MII. A 0 in this bit allows normal MAC operation.

The transmitter and receiver must be disabled before enabling the

loopback mode. (Packets received during MLB mode will reflect loopback

status in the receive descriptor’s

cmdsts.LBP field.)

ATP

Automatic Transmit Padding

Setting this bit to 1 causes the MAC to automatically pad small (runt)

transmit packets to the Ethernet minimum size of 64 bytes. This allows

driver software to transfer only actual packet data. Setting this bit to 0

disables the automatic padding function, forcing software to control runt

padding.

27-24

unused

ECRETRY

Excessive Collision Retry

Enable

This bit enables automatic retries of excessive collisions. If set, the

transmitter will retry the packet up to 4 excessive collision counts, for a total

of 64 attempts. If the packet still does not complete successfully, then the

transmission will be aborted after the 64th attempt. If this bit is not set, then

the transmission will be aborted after the 16th attempt. Note that setting

this bit will change how collisions are reported in the status field of the

transmit descriptor.

22-20

MXDMA

Max DMA Burst Size per Tx

DMA Burst

This field sets the maximum size of transmit DMA data bursts according to

the following table:

000 = 256 32-bit words (1024 bytes)

001 = 2 32-bit words (8 bytes)

010 = 4 32-bit words (16 bytes)

011 = 8 32-bit words (32 bytes)

100 = 16 32-bit words (64 bytes)

101 = 32 32-bit words (128 bytes)

110 = 64 32-bit words (256 bytes)

111 = 128 32-bit word (512 bytes)

BRST_DIS

1000 Mb/s Burst Disable

This bit can disable transmit bursting for 1000 Mb/s half-duplex operation.

The bit will have no affect 10/100 Mb/s or full-duplex modes.

18-16

unused

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