Cs8900a – Cirrus Logic CS8900A User Manual
Page 67
DS271F5
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CS8900A
Crystal LAN™ Ethernet Controller
CIRRUS LOGIC PRODUCT DATASHEET
Register. When reading this register, these bits will be 011000, where the LSB corresponds to
Bit 0.
TxBidErr
If set, the host has commanded the CS8900A to transmit a frame that the CS8900A will not
send. Frames that the CS8900A will not send are:
1) Any frame greater than 1514 bytes, provided that InhibitCRC
(Register 9, TxCMD, Bit C) is clear.
2) Any frame greater than 1518 bytes.
Note that this bit is not set when transmit frames are too short.
Rdy4TxNOW
Rdy4TxNOW signals the host that the CS8900A is ready to accept a frame from the host for
transmission. This bit is similar to Rdy4Tx (Register C, BufEvent, Bit 8) except that there is no
interrupt associated with Rdy4TxNOW. The host can poll the CS8900A and check
Rdy4TxNOW to determine if the CS8900A is ready for transmit. (See Section 5.6 on page 99
for a description of the transmit bid process.)
Reset value is: 0000 0000 0001 1000
4.4.22 Register 19: Test Control
(TestCTL, Read/Write, Address: PacketPage base + 0118h)
TestCTL controls the diagnostic test modes of the CS8900A.
011001
These bits provide an internal address used by the CS8900A to identify this as the Test Control
Register.
DisableLT
When set, the 10BASE-T interface allows packet transmission and reception regardless of the
link status. DisableLT is used in conjunction with the LinkOK (Register 14, LineST, Bit 7) as fol-
lows:
LinkOK DisableLT
0
0
No packet transmission or reception allowed.
Transmitter sends link pulses.
0
1
DisableLT overrides LinkOK to allow packet transmission and
reception.
1
X
Disable has no meaning if LinkOK = 1.
ENDECloop
When set, the CS8900A enters internal loopback mode where the internal Manchester encoder
output is connected to the decoder input. The 10BASE-T and AUI transmitters and receivers
are disabled. When clear, the CS8900A is configured for normal operation.
AUIloop
When set, the CS8900A allows reception while transmitting. This facilitates loopback tests for
the AUI. When clear, the CS8900A is configured for normal AUI operation.
7
6
5
4
3
2
1
0
DisableLT
011001
F
E
D
C
B
A
9
8
FDX
Disable Back-
off
AUIloop
ENDEC loop