LAN9312 datasheet(262/458 Pages) SMSC

262 / 458 page

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

Revision 1.2 (04-08-08)

262

SMSC LAN9312

DATASHEET

Transmit Threshold Mode (TTM)

This bit is used to control the transmit threshold the Host MAC uses as

shown in the two tables in the TR field of this register. This bit is ignored

when the SF bit is set.

This bit should be set to '1' when operating in 10Mbps mode, and cleared

to '0' when operating in 100Mbps mode.

R/W

Store and Forward (SF)

When set, this bit instructs the Host MAC to store a frame of transmit data

before starting transmission.

If this bit is set, the TTM and TR bits (21,13, and 12) are not used.

If this bit is reset, the transmission is started before the entire frame is input

from the HBI (Host Bus Interface). TTM and TR (see bit 21,13, and 12)

determine when the Host MAC initiates the transmission. If the host cannot

keep up, there is a risk of an Underrun Error.

R/W

19:16

TX FIFO Size (TX_FIF_SZ)

This field sets the size of the TX FIFOs in 1KB values to a maximum of

14KB. The TX Status FIFO consumes 512 bytes of the space allocated by

TX_FIF_SIZ, and the TX Data FIFO consumes the remaining space

specified by TX_FIF_SZ. The minimum size of the TX FIFOs is 2KB (TX

Data FIFO and Status FIFO combined). The TX Data FIFO is used for both

TX data and TX commands.

The RX Status and Data FIFOs consume the remaining space, which is

equal to 16KB minus TX_FIF_SIZ. See section Section 9.7.3, "FIFO

Memory Allocation Configuration," on page 121 for more information.

R/W

15:14

RESERVED

13:12

Threshold Control Bits (TR)

This field controls the transmit threshold values the Host MAC should use.

These bits are used when the SF bit is reset. The host can program the

Transmit threshold by setting these bits. The intent is to allow the Host MAC

to start transferring data only after the threshold value is met.

In 10Mbps mode (TTM = 1) the threshold is set as follows:

In 100Mbps mode (TTM = 0) the threshold is set by as follows:

R/W

00b

BITS

DESCRIPTION

TYPE

DEFAULT

[13]

[12]

Threshold (DWORD’s)

012h

018h

020h

028h

[13]

[12]

Threshold (DWORD’s)

020h

040h

080h

100h

LAN9312 Datasheet(PDF) 262 Page - SMSC Corporation

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