AM79C90PC datasheet(29/62 Pages) AMD

29 / 62 page

P R E L I M I N A R Y

AMD

Am79C90

Bit

Name

Description

OWN

This bit indicates that the descriptor

entry is owned by the host (OWN =

O) or by the C-LANCE (OWN = 1).

The host sets the OWN bit after filling

the buffer pointed to by this descrip-

tor. The C-LANCE clears the OWN

bit after transmitting the contents of

the buffer. Neither the host nor the C-

LANCE may alter a descriptor entry

after it has relinquished ownership.

ERR

ERROR summary is the “OR” of

LCOL, LCAR, UFLO or RTRY.

ADD_FCS

Setting ADD_FCS=1, instructs the

controller to append a CRC to this

transmitted frame, regardless of the

setting of the DTCR bit (bit 3 in the

Mode Register). The ADD_FCS bit

allows the controller to be configured

to append CRC on a per packet ba-

sis, when DTCR=1.

ADD_FCS is

only valid when STP=1.

MORE indicates that more than one

retry was needed to transmit a

packet.

ONE

ONE indicates that exactly one retry

was needed to transmit a packet.

The ONE flag is not valid when

LCOL is set.

DEF

DEFERRED

indicates

that

the

C-LANCE had to defer while trying to

transmit a packet. This condition oc-

curs if the channel is busy when the

C-LANCE is ready to transmit.

STP

START OF PACKET indicates that

this is the first buffer to be used by

the C-LANCE for this packet. It is

used for data chaining buffers. STP

is set by the host and is not changed

by the C-LANCE. The STP bit must

be set in the first buffer of the packet,

or the C-LANCE will skip over this

descriptor and poll the next descrip-

tor(s) until the OWN and STP bits

are set.

ENP

END OF PACKET indicates that this

is the last buffer to be used by the C-

LANCE for this packet. It is used for

data chaining buffers. If both STP

and ENP are set, the packet fits into

one buffer and there is no data

chaining. ENP is set by the host and

is not changed by the C-LANCE.

07:00

HADR

The HIGH ORDER 8 address bits of

the buffer pointed to by this descrip-

tor. This field is written by the host

and is not changed by the C-LANCE.

Transmit Message Descriptor 2 (TMD2)

17881B-31

12 11

BCNT

ONES

Bit

Name

Description

15:12

ONES

Must be ones. This field is set by the

host and is not changed by the

C-LANCE.

11:00

BCNT

BUFFER BYTE COUNT is the us-

able length in bytes of the buffer

pointed to by this descriptor ex-

pressed as a negative two’s comple-

ment number. This is the number of

bytes from this buffer that will be

transmitted by the C-LANCE. This

field is written by the host and is not

changed by the C-LANCE. The first

buffer of a packet has to be at least

100 bytes minimum when data

chaining and 64 byte (DTCR = 1) or

60 bytes (DCTR = 0) when not data

chaining.

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