AM79C975VCW datasheet(210/304 Pages) AMD

210 / 304 page

210

Am79C973/Am79C975

P R E L I M INARY

and, therefore, may be set in any

descriptor of a chained buffer

transmission.

ADD_FCS

ADD_FCS dynamically controls

the generation of FCS on a frame

by frame basis. This bit should be

set with the ENP bit. However, for

backward compatibility, it is rec-

ommended that this bit be set for

every descriptor of the intended

frame. When ADD_FCS is set,

the state of DXMTFCS is ignored

and transmitter FCS generation is

activated. When ADD_FCS is

cleared to 0, FCS generation is

controlled by DXMTFCS. When

APAD_XMT (CSR4, bit 11) is set

to 1, the setting of ADD_FCS has

no effect on frames shorter than

64 bytes. ADD_FCS is set by the

host, and is not changed by the

Am79C973/Am79C975

control-

ler. This is a reserved bit in the C-

LANCE (Am79C90) controller.

MORE/LTINT Bit

always

functions

MORE. The value of MORE is

written

the

Am79C973/

Am79C975 controller and is read

by the host. When LTINTEN is

cleared to 0 (CSR5, bit 14), the

Am79C973/Am79C975 controller

will never look at the contents of

bit 28, write operations by the

host have no effect. When LTINT-

EN is set to 1 bit 28 changes its

function to LTINT on host write

operations and on Am79C973/

Am79C975 controller read opera-

tions.

MORE indicates that more than

one retry was needed to transmit

a frame. The value of MORE is

written

the

Am79C973/

Am79C975 controller. This bit

has meaning only if the ENP bit is

set.

LTINT

LTINT is used to suppress inter-

rupts after successful transmis-

sion on selected frames. When

LTINT is cleared to 0 and ENP is

set

the

Am79C973/

Am79C975 controller will not set

TINT (CSR0, bit 9) after a suc-

cessful transmission. TINT will

only be set when the last descrip-

tor of a frame has both LTINT and

ENP set to 1. When LTINT is

cleared to 0, it will only cause the

suppression of interrupts for suc-

cessful transmission. TINT will al-

ways be set if the transmission

has an error. The LTINTEN over-

rides the function of TOKINTD

(CSR5, bit 15).

ONE

ONE indicates that exactly one

retry was needed to transmit a

frame. ONE flag is not valid when

LCOL is set. The value of the

ONE

bit

written

the

Am79C973/Am79C975

control-

ler. This bit has meaning only if

the ENP bit is set.

DEF

Deferred

indicates

that

the

Am79C973/Am79C975 controller

had to defer while trying to trans-

mit a frame. This condition occurs

if the channel is busy when the

Am79C973/Am79C975 controller

is ready to transmit. DEF is set by

the Am79C973/Am79C975 con-

troller and cleared by the host.

STP

Start of Packet indicates that this

is the first buffer to be used by the

Am79C973/Am79C975 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 Am79C973/

Am79C975 controller 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 is not changed by

the Am79C973/Am79C975 con-

troller.

ENP

End of Packet indicates that this

is the last buffer to be used by the

Am79C973/Am79C975 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

not

changed

by the

Am79C973/Am79C975

control-

ler.

BPE

Bus Parity Error is set by the

Am79C973/Am79C975 controller

AM79C975VCW Datenblatt(PDF) 210 Page - Advanced Micro Devices

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