LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers
Table 44. Control Register
Bit
Name
Description
Type 1
Default
R/W
SC
1 = Reset port.
0 = Enable normal operation.
0.15
Reset
0
1 = Enable loopback mode.
0 = Disable loopback mode.
0.14
0.13
Loopback
R/W
R/W
0
Speed
Selection
1 = 100 Mbps.
0 = 10 Mbps.
Note 2
1 = Enable auto-negotiate process (overrides speed select and
duplex mode bits).
0 = Disable auto-negotiate process.
Auto-Negotiation
Enable
0.12
R/W
Note 3
1 = Enable power down.
0 = Enable normal operation.
0.11
0.10
Power Down
Isolate
R/W
R/W
Note 4
Note 5
1 = Electrically isolate port from MII.
0 = Normal operation.
R/W
SC
Restart Auto-
Negotiation
1 = Restart auto-negotiation process.
0 = Normal operation.
0.9
Note 6
1 = Enable full-duplex.
0 = Enable half-duplex.
0.8
Duplex Mode
Collision Test
R/W
R/W
RO
Note 7
Note 8
1 = Enable COL signal test.
0 = Disable COL signal test.
0.7
Transceiver Test
Mode
0.6:4
0.3
Not supported.
Not supported.
0
0
Master-Slave
Enable
RO
0.2
Master-Slave Value Not supported.
Reserved Write as 0; ignore on read.
RO
0
0.1:0
R/W
N/A
1. R/W = Read/Write
RO = Read Only
SC = Self Clearing
2. If auto-negotiation is enabled, this bit is ignored. If auto-negotiation is disabled, the default value of bit 0.13 is determined by
CFG_0.
3. If SD_TXn is tied High or to a 5V PECL input (FX Mode), the default value of bit 0.12 = 0. If SD_TXn is tied Low (TP Mode),
the default value of bit 0.12 is determined by AUTOENA.
4. The LXT974/975 internally holds all set values of the configuration registers upon exiting power down mode. A delay of 500
ns minimum is required from the time power down is cleared until any register can be written.
5. The default value of bit 0.10 is determined by pin TRSTEn.
6. If auto-negotiation is enabled, the default value of bit 0.9 is determined by CFG_0.
If auto-negotiation is disabled, the bit is ignored.
7. If auto-negotiation is enabled, this bit is ignored. If auto-negotiation is disabled and the port is operating in TX mode, the
default value of bit 0.8 is determined by pin FDE. If auto-negotiation is disabled and the port is operating in FX mode, the
default value of bit 0.8 is determined by pin FDE_FX.
8. This bit is ignored unless loopback is enabled (bit 0.14 = 1).
64
Datasheet
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