AM79C970A datasheet(168/219 Pages) AMD

168 / 219 page

AMD

P R E L I M I N A R Y

168

Am79C970A

start of a new frame and starts a

new transmission.

UFLO is set by the PCnet-PCI II

controller

and

cleared

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). Excessive

Deferral will also set the interrupt

bit EXDINT (CSR5, bit 7).

LCOL

Late Collision indicates that a

collision has occurred after the

first slot time of the channel has

elapsed. The PCnet-PCI II con-

troller does not retry on late

collisions.

LCOL

set

the PCnet-PCI II controller and

cleared by the host.

LCAR

Loss of Carrier is set when

the

carrier

lost

during

a PCnet-PCI II controller-initiated

transmission when in AUI or

GPSI mode and the device is op-

erating in half-duplex mode. The

PCnet-PCI II controller does not

retry upon loss of carrier. It will

continue to transmit the whole

frame until done. LCAR will not

be set when the device is operat-

ing in full-duplex mode and the

AUI or GPSI port is active. LCAR

is not valid in Internal Loopback

Mode.

LCAR

set

the PCnet-PCI II controller and

cleared by the host.

In 10BASE-T mode, LCAR will

be set when the T-MAU was

Link

Fail

state

during

the transmission.

RTRY

Retry error indicates that the

transmitter has failed after 16 at-

tempts to successfully transmit a

message, due to repeated colli-

sions on the medium. If DRTY is

set to ONE in the MODE register,

RTRY will set after 1 failed trans-

mission attempt. RTRY is set by

the PCnet-PCI II controller and

cleared by the host.

25–16

TDR

Time Domain Reflectometer re-

flects the state of an internal

PCnet-PCI II controller counter

that counts at a 10 MHz rate from

the start of a transmission to the

occurrence of a collision or loss

of carrier. This value is useful in

determining

the

approximate

distance to a cable fault. The

TDR value is written by the

PCnet-PCI II 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

useful. This feature is here

primarily

maintain

full

compatibility with the C-LANCE

device (Am79C90).

15–4

RES

Reserved locations.

3–0

TRC

Transmit Retry Count. Indicates

the number of transmit retries

of the associated packet. The

maximum 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

interpreted as meaning 16. TRC

is written by the PCnet-PCI II

controller into the last transmit

descriptor of a frame, or when

an error terminates a frame.

Valid only when OWN is cleared

to ZERO.

TMD3

Bit

Name

Description

31–0

RES

Reserved locations.

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