CS8900A
Crystal LAN™ ISA Ethernet Controller
5.7.11 Transmit Frame Length
this situation is described in the following para-
graphs.
The length of the frame transmitted is determined
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 35 defines how
these bits affect the length of the transmit frame. In
addition, it shows which frames the CS8900A will
send.
The original IEEE 802.3 specification requires the
MAC to wait until 4 valid link-pulses are received
before asserting Link-OK. Any time an invalid
link-pulse is received, the count is restarted. When
auto-negotiation occurs, a transmitter sends FLPs
(auto-negotiation Fast Link Pulses) bursts instead
of the original IEEE 802.3 NLP (Normal Link
Pulses).
If the hub is attempting to auto-negotiate with the
CS8900A, the CS8900A will never get more than 1
"valid" link pulse (valid NLP). This is not a prob-
lem if the CS8900A is already sending link-pulses,
because when the hub receives NLPs from the
CS8900A, the hub is required to stop sending FLPs
and start sending NLPs. The NLP transmitted by
the hub will put the CS8900A into Link-OK.
5.8 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 (reg-
ister 8).
However, if the CS8900A is in Auto-Switch mode,
the CS8900A will never send any link-pulses, and
the hub will never change from sending FLPs to
sending NLPs.
5.9 Auto-Negotiation Considerations
When the CS8900A is connected to an auto negoti-
ation hub, and if auto-media detection is selected
(bits 8 and 9 of register 13), then the CS8900A may
not auto-select the 10BASE-T media. The cause of
Register 9, TxCMD
Host specified transmit length at 0146h (in bytes)
60 < TxLength < 1514 < TxLength < 1518 TxLength > 1518
TxPad- InhibitCRC 3 < TxLength < 60
Dis (Bit D)
(Bit C)
1514
0
0
Pad to 60 and add Send frame and add
Will not send
Will not send
Will not send
Will not send
CRC
CRC [Normal Mode]
0
1
1
0
Pad to 60 and
send without CRC
Send frame without
CRC
Send frame without
CRC
Send without
pads, and add
CRC
Send frame and add
CRC
Will not send
1
1
Send without
pads and without
CRC
Send frame without
CRC
Send frame without
CRC
Wiill not send
Notes: 8. If the TxPadDis bit is clear and InhibitCRC is set and the CS8900A is commanded to send a frame of
length less than 60 bytes, the CS8900A pads.
9. The CS8900A will not send a frame with TxLength less than 3 bytes.
Table 35. Transmit Frame Length
CIRRUS LOGIC PRODUCT DATA SHEET
DS271PP3
105
CIRRUS [ CIRRUS LOGIC ]
