AM79C970 datasheet(129/168 Pages) AMD

129 / 168 page

AMD

P R E L I M I N A R Y

1-996

Am79C970

before the end of the frame was

reached. Upon UFLO error, the

transmitter is turned off (CSR0,

TXON = 0). UFLO is set by the

PCnet-PCI

controller

and

cleared by the host.

EXDEF

Excessive

Deferral.

Indicates

that the transmitter has experi-

enced Excessive Deferral on this

transmit frame, where Excessive

Deferral is defined in ISO 8802-3

(IEEE/ANSI 802.3).

LCOL

LATE COLLISION indicates that

a collision has occurred after the

slot time of the channel has

elapsed. The PCnet-PCI control-

ler does not re-try on late colli-

sions. LCOL is set by the

PCnet-PCI

controller

and

cleared by the host.

LCAR

LOSS OF CARRIER is set when

the carrier is lost during an

PCnet-PCI

controller-initiated

transmission when in AUI mode.

The PCnet-PCI controller does

not re-try upon loss of carrier. It

will continue to transmit the

whole frame until done. LCAR is

not valid in Internal Loopback

Mode. LCAR is set by the PCnet-

PCI controller and cleared by the

host.

In 10BASE-T mode, LCAR will

be set when T-MAU is in link fail

state.

RTRY

RETRY ERROR indicates that

the transmitter has failed after 16

attempts to successfully transmit

a message, due to repeated colli-

sions on the medium. If DRTY = 1

in the MODE register, RTRY will

set after 1 failed transmission

attempt. RTRY is set by the

PCnet-PCI

controller

and

cleared by the host.

ONE,

MORE, and RTRY are mutually

exclusive.

25–16

TDR

TIME

DOMAIN

REFLE-

CTOMETRY reflects the state of

an internal PCnet-PCI controller

counter that counts at a 10 MHz

rate from the start of a transmis-

sion to the occurrence of a colli-

sion or loss of carrier. This value

is useful in determining the ap-

proximate distance to a cable

fault. The TDR value is written by

the PCnet-PCI controller and is

valid only if RTRY is set.

Note that 10 MHz gives very low

resolution and in general has not

been found to be particularly use-

ful. This feature is here primarily

to maintain full compatibility with

the LANCE device (Am7990).

15–4

RES

Reserved locations.

3–0

TRC

Transmit Retry Count. Indicates

the number of transmit retries of

the associated packet. The maxi-

mum count is 15. However, if a

RETRY error occurs, the count

will roll over to ZERO. In this case

only, the Transmit Retry Count

value of ZERO should be inter-

preted as meaning 16. TRC is

written by the PCnet-PCI control-

ler into the last transmit descrip-

tor of a frame, or when an error

terminates a frame. Valid only

when OWN = 0.

TMD3

Bit

Name

Description

31–0

RES

Reserved locations.

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