LAN83C183 Datasheet, PDF (35/113 Pages) SMSC Corporation – FAST ETHERNET PHYSICAL LAYER DEVICE

1.2.13 Collision
Collisions occur whenever transmit and receive operations occur simultaneously
while the device is in Half-Duplex mode.
1.2.13.1 100 MBITS/S
In 100 Mbits/s operation, a collision occurs and is sensed whenever there is
simultaneous transmission (packet transmission on TPO+/-) and reception (non-idle
symbols detected at the TPI+/- input). When a collision is detected, the COL output
is asserted, TP data continues to be transmitted on the twisted-pair outputs, TP data
continues to be received on the twisted-pair inputs, and internal CRS loopback is
disabled. After a collision is in process, CRS is asserted and stays asserted until the
receive and transmit packets that caused the collision are terminated.
The collision function is disabled if the device is in the Full-Duplex mode, is in the
Link Fail state, or if the device is in the diagnostic loopback mode.
1.2.13.2 10 MBITS/S
A collision in the 10 Mbits/s mode is identical to one the 100 Mbits/s mode except:
• The 10 Mbits/s squelch criteria determines reception
• The RXD[3:0] outputs are all forced LOW
• The collision signal (COL) is asserted when the SQE test is performed
• The collision signal (COL) is asserted when the jabber condition has been
detected.
1.2.13.3 COLLISION TEST
To test the Controller Interface collision signal (COL), set the COLTST bit in the MI
serial port Control register. When this bit is set, TX_EN is looped back onto COL and
the TP outputs are disabled.
1.2.13.4 COLLISION INDICATION
Collisions are indicated through the COL pin, which is asserted HIGH every time a
collision occurs. The device can also be programmed to indicate collisions on the
PLED2n output.
In the MI serial port Configuration 2 register, set the LED function select bits
(LED_DEF_[1:0]) so that collision activity is indicated at the PLED2n output. Set the
PLED2_[1:0] bits in the same register to 0b11 (normal). With these settings, a LED
connected to the PLED2n pin will reflect collision activity.
When the PLED2n pin is programmed to be a collision detect output, it is asserted
LOW for 100 ms every time a collision occurs. The PLED2n output is open drain with
a pullup resistor and can drive an LED from V_DD or can drive another digital input.
See Section 1.2.14, “LED Drivers,” page 1-36 for more details on how to program the
LED output pins to indicate various conditions.
SMSC DS – LAN83C183
35
Rev. 12/14/2000