AX88140AP datasheet(21/46 Pages) ASIX

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AX88140A

PRELIMINARY

ASIX ELECTRONICS CORPORATION

4.2 Host REGs

4.2.1 Bus Mode Register (REG0)

FIELD

R/W/C

DESCRIPTION

31:22

RESERVED

R/W

RML - Read Multiple

When set, the AX88140A supports the memory-read-multiple command on the PCI bus. This bus

command is used in memory read bursts with more than one longword. When reset, the AX88140A

uses memory-read command in all its memory read accesses on the PCI bus.

R/W

DBO - Descriptor Byte Ordering Mode

When set, the AX88140A operates in big edian ordering mode for descriptors only.

When reset, the AX88140A operates in little endian mode.

19:14

Reserved.--Written as “0” for future compatibility concern.

13:8

R/W

PBL - Programmable Burst Length

Indicates the maximum number of longwords to be transfered in one DMA transaction. If reset, the

ax88140a burst is limited only by the amount of data stored in the receive FIFO (at least 16 longword),

or by the amount of free space in the transmit FIFO (at least 16 longword) before issuing a bus request.

The PBL can be programmed with permissible values 0,1,2,4,8,16, or 32. After reset, the PBL default

value is 0.

R/W

BLE - Big/Little Endian

When set, the AX88140A operates in big endian byte ordering mode. When reset, the AX88140A

operates in little endian byte ordering mode. Big endian is applicable only for data buffer

6:2

RESERVED

R/W

BAR - Bus Arbitration

Selects the internal bus arbitration between the receive and transmit processes.

When set, a round robin arbitration scheme is applied resulting in equal sharing between processes.

When reset, the receive process has priority over the transmit process, unless the ax88140a is currently

transmitting.

R/W

SWR - Software Reset

When set, the AX88140A resets all internal hardware with the exception of the configuration area and

also, it does not change the port select setting (REG6<18>).

Software reset does not affect the configuration area.

Tab - 15 REG0 Bus Mode Register Description

4.2.2 Transmit Poll Demand (REG1)

FIELD

R/W

DESCRIPTION

31:0

TPD - Transmit Poll Demand

When written with any value, the AX88140A checks for frames to be transmitted. If no descriptor is

available, the transmit process returns to the suspended states and REG5<2> is asserted. If the descriptor

is available the transmit process resumes.

Tab - 16 REG1 Transmit Poll Demand Register Description

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