CS8900A
Crystal LAN™ ISA Ethernet Controller
4.4.22 Register 19: Test Control
(TestCTL, Read/Write, Address: PacketPage base + 0118h)
7
6
5
4
3
2
1
0
8
DisableLT
011001
F
E
D
C
B
A
9
Disable Back-
off
FDX
AUIloop
ENDEC loop
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
0
DisableLT
0
No packet transmission for reception
allowed. Transmitter sends link impulses.
0
1
DisableLT overrides LinkOK to allow packet
transmission and reception. Transmitter
does not send link pulses.
1
N/A
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.
Disable Backoff
FDX
When set, the backoff algorithm is disabled. The CS8900A transmitter looks only for completion
of the inter packet gap before starting transmission. When clear, the backoff algorithm is used.
When set, 10BASE-T full duplex mode is enabled and CRS (Register 14, LineST, Bit E) is ig-
nored. This bit must be set when performing loopback tests on the 10BASE-T port. When clear,
the CS8900A is configured for standard half-duplex 10BASE-T operation.
At reset, if no EEPROM is found by the CS8900A, then the register has the following initial state. If an EEPROM is
found, then the register’s initial value may be set by the EEPROM. See Section 3.3 on page 19.
Reset value is: 0000 0000 0001 1001
CIRRUS LOGIC PRODUCT DATA SHEET
DS271PP3
69
CIRRUS [ CIRRUS LOGIC ]
