adm6996f Infineon Technologies Corporation, adm6996f Datasheet - Page 25

• Manufacturer Part Number: adm6996f
• Description: 6 Port 10/100 Mb/s Single Chip Ethernet Switch Controller
• Manufacturer: Infineon Technologies Corporation

ADM6996F
Infineon-ADMtek Co Ltd.
3.7
3.8
3.9
and timing measurements (as specified in the IEEE 802.3 10Base-T standard) to
determine the validity of data on the twisted-pair inputs.
The signal at the start of the packet is checked by the analog squelch circuit and any
pulses not exceeding the squelch level (either positive or negative, depending upon
polarity) will be rejected. Once this first squelch level is overcome correctly, the opposite
squelch level must then be exceeded within 150ns. Finally, the signal must exceed the
original squelch level within an additional 150ns to ensure that the input waveform will
not be rejected.
Only after all these conditions have been satisfied will a control signal be generated to
indicate to the remainder of the circuitry that valid data is present.
Valid data is considered to be present until the squelch level has not been generated for a
time longer than 200 ns, indicating end of packet. Once good data has been detected, the
squelch levels are reduced to minimize the effect of noise, causing premature end-of-
packet detection. The receive squelch threshold level can be lowered for use in longer
cable applications. This is achieved by setting bit 10 of register address 11h.
Carrier Sense
Carrier Sense (CRS) is asserted due to receive activity once valid data is detected via the
smart squelch function. For 10 Mbits/s half duplex operation, CRS is asserted during
either packet transmission or reception. For 10 Mbits/s full duplex and repeater mode
operations, the CRS is asserted only due to receive activity.
Jabber Function
The jabber function monitors the ADM6996F output and disables the transmitter if it
attempts to transmit a longer than legal sized packet. If TXEN is high for greater than
24ms, the 10Base-T transmitter will be disabled. Once disabled by the jabber function,
the transmitter stays disabled for the entire time that the TXEN signal is asserted. This
signal has to be de-asserted for approximately 256 ms (The un-jab time) before the jabber
function re-enables the transmit outputs. The jabber function can be disabled by
programming bit 4 of register address 10h to high.
Link Test Function
A link pulse is used to check he integrity of the connection with the remote end. If valid
link pulses are not received, the link detector disables the 10Base-T twisted-pair
transmitter, receiver, and collision detection functions.
The link pulse generator produces pulses as defined in IEEE 802.3 10Base-T standard.
Each link pulse is nominally 100ns in duration and is transmitted every 16 ms, in the
absence of transmit data.
Function Description
3-7