CS89712 datasheet(66/170 Pages) CIRRUS

66 / 170 page

CS89712

DS502PP2

If the CS89712 commits buffer space to a particular

transmit frame, it will not allow subsequent frames

to be written to that buffer space as long as the

transmit frame is committed.

After buffer space is committed, the frame is sub-

sequently transmitted unless any of the following

occur:

1) The software completely writes the frame data,

but transmission failed on the Ethernet line.

There are three such failures, and these are in-

dicated by three bits in the TxEvent register:

16coll, Jabber, or Out-of-Window.

or:

2) The software aborts the transmission by setting

the Force (TxCMD register bit 8) bit. In this

case, the committed transmit frame, as well as

any yet-to-be-transmitted frames queued in the

on-chip memory, are cleared and not transmit-

ted. The software should make TxLength = 0

when using the Force bit.

or:

3) There is a transmit under-run while the Tx-

Underrun bit (BufEvent register bit 9) is set.

Successful transmission is indicated when the

TxOK bit (TxEvent register bit 8) is set.

2.34.11 Transmit Frame Length

The length of the frame transmitted is determined

by the value written into the TxLength register

during the Transmit Request. The length of the

transmit frame may be modified by the configura-

tion of the TxPadDis bit (TxCMD register bit D)

and the InhibitCRC bit (TxCMD register bit C).

Table 30 defines how these bits affect the length of

the transmit frame, and details which frames will

be sent.

2.35 Full Duplex Considerations

The driver should not bid to transmit a long frame

(i.e., a frame greater than 118 bytes) if the prior

transmit frame is still being transmitted. The end of

the transmission of this prior frame is indicated by

a TxOK bit being set in the TxEvent register.

TxCMD register

Software specified transmit length at 0146h (in bytes)

TxPadDis

(Bit D)

InhibitCRC

(Bit C)

3 < TxLength

< 60

60 < TxLength

< 1514

1514 < TxLength

< 1518

TxLength

> 1518

Pad to 60 and add

CRC

Send frame and add

CRC [Normal Mode]

Will not send

Pad to 60 and send

without CRC

Send frame without

CRC

Send frame

without CRC

Will not send

Send without pads,

and add CRC

Send frame and add

CRC

Will not send

Send without pads

and without CRC

Send frame without

CRC

Send frame

without CRC

Will not send

Notes: 1. If the TxPadDis bit is clear and InhibitCRC is set and the CS89712 is commanded to send a frame of

length less than 60 bytes, the CS89712 pads.

2. The CS89712 will not send a frame with TxLength less than 3 bytes.

Table 30. Transmit Frame Length

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