CS8900 View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
CS8900 Datasheet PDF : 132 Pages
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CS8900
1. The host must issues a Transmit Request;
2. The Transmit Request must be successful; and,
3. Either the host reads that the Rdy4TxNOW bit
(Register 18, BusST, Bit 8) is set, or the host
reads that the Rdy4Tx bit (Register C,
BufEvent, bit 8) is set.
If the CS8900 commits buffer space to a particu-
lar 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
subsequently transmitted unless any of the fol-
lowing occur:
1. The host completely writes the frame data, but
transmission failed on the Ethernet line. There
are three such failures, and these are indicated
by three transmit error bits in the TxEvent
register (Register 8): 16coll, Jabber, or Out-
of-Window.
Or:
2. The host aborts the transmission by setting the
Force (Register 9, TxCMD, 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
transmitted. The host should make TxLength
= 0 when using the Force bit.
Or:
3. There is a transmit under-run, and the TxUn-
derrun bit (Register C, BufEvent, Bit 9) is set.
Successful transmission is indicated when the
TxOK bit (Register 8, TxEvent, Bit 8) is set.
5.7.11 Transmit Frame Length
The length of the frame transmitted is deter-
mined by the value written into the TxLength
register (PacketPage base + 0146h) during the
Transmit Request. The length of the transmit
frame may be modified by the configuration of
the TxPadDis bit (Register 9, TxCMD, Bit D)
and the InhibitCRC bit (Register 9, TxCMD, Bit
C). Table 5.17 defines how these bits affect the
length of the transmit frame. In addition, it
shows which frames the CS8900 will send.
Register 9, TxCMD
TxPadDis InhibitCRC
(Bit D)
(Bit C)
0
0
0
1
1
0
1
1
Host specified transmit length at 0146h (in bytes)
3 < TxLength < 60 60 > TxLength < 1514 1514 > TxLength < 1518 TxLength > 1518
Pad to 60
and add CRC
Pad to 60 and
send without CRC
Send without pads,
and add CRC
Send without pads
and without CRC
Send frame and add
CRC [Normal Mode]
Send frame
without CRC
Send frame
and add CRC
Send frame
without CRC
Will not send
Send frame
without CRC
Will not send
Send frame
without CRC
Will not send
Will not send
Will not send
Will not send
Notes: 1. If the TxPadDis bit is clear and InhibitCRC is set and the CS8900 is commanded to send a frame of
length less than 60 bytes, the CS8900 pads.
2. The CS8900 will not send a frame with TxLength less than 3 bytes.
Table 5.17. Transmit Frame Length
DS150PP2
105
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