Cirrus Logic CS8900A - Manual (Page 106)

106 DS271F5
CS8900A
Crystal LAN™ Ethernet Controller
CIRRUS LOGIC PRODUCT DATASHEET
CS8900A may not auto-select the 10BASE-T
media. The cause of this situation is described
in the following paragraphs.
The original IEEE 802.3 specification requires
the MAC to wait until 4 valid link-pulses are re-
ceived before asserting Link-OK. Any time an
invalid link-pulse is received, the count is re-
started. 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 problem if the CS8900A is already
sending link-pulses, because when the hub re-
ceives NLPs from the CS8900A, the hub is re-
quired 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.
Register 9, TxCMD Host specified transmit length at 0146h (in bytes)
TxPad-
Dis (Bit D)
InhibitCRC
(Bit C)
3 < TxLength < 60 60 < TxLength <
1514
1514 < TxLength < 1518 TxLength > 1518
0 0 Pad to 60 and add
CRC
Send frame and add
CRC [Normal Mode]
Will not send Will not send
0 1 Pad to 60 and
send without CRC
Send frame without
CRC
Send frame without
CRC
Will not send
1 0 Send without
pads, and add
CRC
Send frame and add
CRC
Will not send Will not send
1 1 Send without
pads and without
CRC
Send frame without
CRC
Send frame without
CRC
Will 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 36. Transmit Frame Length