Small Footprint MII/RMII 10/100 Ethernet Transceiver for Automotive Applications
Datasheet
3.2.3
3.2.4
Disabling Auto-Negotiation
Auto-negotiation can be disabled by setting the Auto-Negotiation Enable bit of the Basic Control
Register to zero. The device will then force its speed of operation to reflect the information in the Basic
Control Register (Speed Select bit and Duplex Mode bit). These bits should be ignored when auto-
negotiation is enabled.
Half vs. Full Duplex
Half duplex operation relies on the CSMA/CD (Carrier Sense Multiple Access / Collision Detect)
protocol to handle network traffic and collisions. In this mode, the carrier sense signal, CRS, responds
to both transmit and receive activity. If data is received while the transceiver is transmitting, a collision
results.
In full duplex mode, the transceiver is able to transmit and receive data simultaneously. In this mode,
CRS responds only to receive activity. The CSMA/CD protocol does not apply and collision detection
is disabled.
3.3
HP Auto-MDIX Support
HP Auto-MDIX facilitates the use of CAT-3 (10BASE-T) or CAT-5 (100BASE-T) media UTP
interconnect cable without consideration of interface wiring scheme. If a user plugs in either a direct
connect LAN cable, or a cross-over patch cable, as shown in Figure 3.2, the device’s Auto-MDIX
transceiver is capable of configuring the TXP/TXN and RXP/RXN pins for correct transceiver operation.
The internal logic of the device detects the TX and RX pins of the connecting device. Since the RX
and TX line pairs are interchangeable, special PCB design considerations are needed to accommodate
the symmetrical magnetics and termination of an Auto-MDIX design.
The Auto-MDIX function can be disabled via the AMDIXCTRL bit in the Special Control/Status
Indications Register.
RJ-45 8-pin straight-through
for 10BASE-T/100BASE-TX
signaling
RJ-45 8-pin cross-over for
10BASE-T/100BASE-TX
signaling
TXP
TXN
RXP
TXP
TXP
TXN
TXP
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
1
2
3
4
5
6
7
8
TXN
TXN
2
3
4
5
6
7
8
RXP
RXP
RXP
Not Used
Not Used
RXN
Not Used
Not Used
RXN
Not Used
Not Used
RXN
Not Used
Not Used
RXN
Not Used
Not Used
Not Used
Not Used
Not Used
Not Used
Not Used
Not Used
Direct Connect Cable
Cross-Over Cable
Figure 3.2 Direct Cable Connection vs. Cross-over Cable Connection
Revision 1.1 (05-26-10)
30
SMSC LAN88710AM/LAN88710BM
DATASHEET
SMSC [ SMSC CORPORATION ]
