LAN83C171 datasheet(39/90 Pages) SMSC

39 / 90 page

DMA DESCRIPTOR BITS DESCRIPTION

TRANSMIT DMA DESCRIPTOR BITS DESCRIPTION

The following diagram shows the format of the transmit descriptor table:

TX LENGTH

TX STATUS

dword 0

BUFFER ADDRESS

dword 1

CONTROL

BUF LENGTH

dword 2

NEXT DESCRIPTOR ADDRESS

dword 3

DWORD 0 - STATUS/LENGTH Bit Number

Description

31 through 16: Transmit Length

15 - OWNER: Descriptor ownership bit - set

to 0 when the host owns the descriptor, 1

when the NIC owns the descriptor.

14 and 13 - Reserved.

12 through 8 -

COLLISION COUNT: These

bits contain the number of collisions detected

while

attempting

transmit

the

current

packet. Bit 12 also indicates transmit abort

for excessive collisions.

7 -

DEFERRING: This bit is set when the

interframe gap state machine is deferring. If

the PHY has asserted the collision line as a

result of jabber, this bit will stay set indicating

the jabber condition. Otherwise, returns 0.

6 - OUT OF WINDOW COLLISION: This bit is

set if a collision is detected more than one slot

time

after

the

start

transmission.

Transmission

aborted

under

these

conditions.

5 - COLLISION DETECT HEARTBEAT: This bit is

set to a '1' during transmission of each packet. It

is set to '0' if a collision is detected within 36 bit

times of the end of each packet transmission. If

no collision is detected within this window, it

remains '1'.

This bit always returns zero in full

duplex mode.

4 - UNDERRUN: This bit is set when the transmit

DMA is unable to supply the transmitter enough

data to maintain frame transmission. Otherwise,

returns 0.

3 - CARRIER SENSE LOST: This bit is set if the

carrier is lost during packet transmission. Carrier

sense is monitored from its rising edge at the start

of the outgoing frame's echo. Transmission is not

aborted upon loss of carrier. This bit will always

return zero in full duplex mode.

2 - TRANSMITTED WITH COLLISIONS:

When

set, this bit indicates the frame collided at least

once with another frame on the network. It is not

set

for

either

out-of-window

collisions

excessive collision aborts.

LAN83C171 데이터시트(PDF) 39 Page - SMSC Corporation

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