AM79C970 datasheet(128/168 Pages) AMD

128 / 168 page

P R E L I M I N A R Y

AMD

1-995

Am79C970

(Am7990). This function differs

from the ILACC function for this

bit.

NO_FCS

NO_FCS dynamically controls

the generation of FCS on a frame

by frame basis. It is valid only if

the

ENP

bit

set.

When

NO_FCS is set, the state of

DXMTFCS is ignored and trans-

mitter FCS generation is deacti-

vated. When NO_FCS = 0, FCS

generation

controlled

DXMTFCS. NO_FCS is set by

the host, and unchanged by the

PCnet-PCI controller. This was a

reserved

bit

the

LANCE

(Am7990). This function is iden-

tical to the ILACC function for this

bit

MORE indicates that more than

one re-try was needed to trans-

mit a frame. The value of MORE

is written by the PCnet-PCI con-

troller. This bit has meaning only

if the ENP bit is set. ONE, MORE,

and

RTRY

are

mutually

exclusive.

ONE

ONE indicates that exactly one

re-try was needed to transmit a

frame. ONE flag is not valid when

LCOL is set. The value of the

ONE bit is written by the PCnet-

PCI controller. This bit has mean-

ing only if the ENP bit is set.

ONE, MORE, and RTRY are mu-

tually exclusive.

DEF

DEFERRED indicates that the

PCnet-PCI controller had to de-

fer while trying to transmit a

frame. This condition occurs if

the channel is busy when the

PCnet-PCI controller is ready to

transmit. DEF is set by the

PCnet-PCI

controller

and

cleared by the host.

STP

START OF PACKET indicates

that this is the first buffer to be

used by the PCnet-PCI controller

for this frame. It is used for data

chaining buffers. The STP bit

must be set in the first buffer of

the frame, or the PCnet-PCI con-

troller will skip over the descriptor

and poll the next descriptor(s)

until the OWN and STP bits

are set.

STP is set by the host and un-

changed

the

PCnet-PCI

controller.

ENP

END OF PACKET indicates that

this is the last buffer to be used by

the PCnet-PCI controller for this

frame. It is used for data chaining

buffers. If both STP and ENP are

set, the frame fits into one buffer

and there is no data chaining.

ENP is set by the host and un-

changed

the

PCnet-PCI

controller.

23–16

RES

Reserved locations.

15–12 ONES

MUST BE ONES. This field is

written by the host and un-

changed

the

PCnet-PCI

controller.

11–00 BCNT

BUFFER BYTE COUNT is the

usable

length

the

buffer

pointed to by this descriptor, ex-

pressed as the two’s comple-

ment of the length of the buffer.

This is the number of bytes from

this buffer that will be transmitted

by the PCnet-PCI controller. This

field is written by the host and un-

changed by the PCnet-PCI con-

troller. There are no minimum

buffer size restrictions.

TMD2

Bit

Name

Description

BUFF

BUFFER ERROR is set by the

PCnet-PCI

controller

during

transmission when the PCnet-32

controller does not find the ENP

flag in the current buffer and does

not own the next buffer. This can

occur in either of two ways:

The OWN bit of the next

buffer is ZERO.

FIFO underflow occurred

before the PCnet-PCI

controller obtained the

STATUS byte

(TMD1[31:24]) of the next

descriptor. BUFF is set by

the PCnet-PCI controller and

cleared by the host. BUFF

error will turn off the trans-

mitter (CSR0, TXON = 0).

If a Buffer Error occurs, an Un-

derflow Error will also occur.

BUFF is not valid when LCOL or

RTRY error is set during transmit

data chaining. BUFF is set by the

PCnet-PCI

controller

and

cleared by the host.

UFLO

UNDERFLOW

ERROR

indi-

cates that the transmitter has

truncated a message due to data

late from memory. UFLO indi-

cates that the FIFO has emptied

AM79C970 Datasheet(PDF) 128 Page - Advanced Micro Devices

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