CS8900-CQ3 Cirrus Logic, CS8900-CQ3 Datasheet - Page 105

• Manufacturer Part Number: CS8900-CQ3
• Description: Crystal LAN ISA Ethernet Controller
• Manufacturer: Cirrus Logic

DS271PP3
5.7.11 Transmit Frame Length
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.
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).
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
CS8900A
Crystal LAN™ ISA Ethernet Controller
Notes: 8. If the TxPadDis bit is clear and InhibitCRC is set and the CS8900A is commanded to send a frame of
Dis (Bit D)
TxPad-
Register 9, TxCMD
0
0
1
1
9. The CS8900A will not send a frame with TxLength less than 3 bytes.
InhibitCRC
length less than 60 bytes, the CS8900A pads.
(Bit C)
0
1
0
1
3 < TxLength < 60
Pad to 60 and add
send without CRC
pads and without
pads, and add
Pad to 60 and
Send without
Send without
CRC
CRC
CRC
CIRRUS LOGIC PRODUCT DATA SHEET
Table 35. Transmit Frame Length
Host specified transmit length at 0146h (in bytes)
Send frame and add
Send frame and add
CRC [Normal Mode]
Send frame without
Send frame without
60 < TxLength <
1514
CRC
CRC
CRC
this situation is described in the following para-
graphs.
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.
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.
1514 < TxLength < 1518
Send frame without
Send frame without
Will not send
Will not send
CRC
CRC
TxLength > 1518
Will not send
Will not send
Will not send
Wiill not send
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