DP83934CVUL20 National Semiconductor, DP83934CVUL20 Datasheet - Page 13

• Manufacturer Part Number: DP83934CVUL20
• Manufacturer: National Semiconductor

Specifications of DP83934CVUL20

• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (max): 5.25V
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 160
• Lead Free Status / RoHS Status: Not Compliant

3 0 Functional Description
The signal at the start of the packet is checked by the smart
squelch 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
150 ns Finally the signal must exceed the original squelch
level within the next 150 ns time period to ensure that the
input waveform will not be rejected The checking proce-
dure typically results in the loss of three bits at the begin-
ning of each packet
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 At this time the smart
squelch circuitry is reset
In the reduced squelch mode the operation is identical ex-
cept that the lower squelch levels shown in Figure 3-2 are
used
Valid data is considered to be present until either squelch
level has not been generated for a time period of more than
150 ns indicating the 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 detec-
tion
Collision A collision is detected by the TPI module when
the receive and transmit channels are simultaneously ac-
tive If the TPI is receiving when a collision is detected it is
reported to the controller immediately If however the TPI
is transmitting when a collision is detected the collision is
not reported until seven bits have been received while in the
collision state This prevents a collision being reported in-
correctly due to noise on the network The signal to the
controller remains for the duration of the collision
Approximately 1 s after the transmission of each packet a
signal called the Signal Quality Error (SQE) is generated
which typically consists of 10 cycles of a 10 MHz signal
This 10 MHz signal also called the Heartbeat ensures the
continued functioning of the collision circuitry
Link Detector Generator The link generator is a timer cir-
cuit that generates a link pulse produced by the transmitter
section as defined by the 10BASE-T specification The
100 ns wide pulse is transmitted on the TXO
16 ms in the absence of transmit data
This link pulse is used to check the integrity of the connec-
tion to the remote MAU The link detection circuit checks for
valid pulses that are received from the remote unit If valid
link pulses are not received the link detector will disable the
transmit receive and collision detection functions
The LINKLED output can directly drive a LED to show that
there is a good twisted pair link For normal conditions the
LED will be on The link integrity function can be disabled by
asserting the LNKDIS input pin
Jabber The jabber timer monitors the transmitter and dis-
ables the transmission if the transmitter is active for greater
than 26 ms The transmitter is then disabled for the whole
time that the ENDEC module’s internal transmit enable is
asserted This signal has to be deasserted for approximate-
ly 750 ms (the unjab time) before the Jabber re-enables the
transmit outputs
a
(Continued)
output every
13
Transmitter The transmitter consists of four signals the
true and complement Manchester encoded data (TXO
and these signals delayed by 50 ns (TXOd
These four signals are resistively combined (see Section
8 2) TXO
figuration referred to as pre-emphasis This digital pre-em-
phasis is required to compensate for the low-pass filter ef-
fects of the twisted pair cable which causes greater attenua-
tion to the 10 MHz (50 ns) pulses of the Manchester encod-
ed waveform than the 5 MHz (100 ns) pulses
The signal with pre-emphasis is generated by resistively
combining TXO
along with its complement is passed to the transmit filter
Status Information Status information is provided by the
SONIC-T Controller on the RXLED
LINKLED and POLED outputs as described in the pin de-
scription table These outputs (Figure 3-4) are suitable for
driving status LEDs
FIGURE 3-3 Typical Summed Transmit Waveform
FIGURE 3-4 Typical SONIC-T LED Connection
a
with TXOd
a
and TXOd
b
and TXO
b
(Figure 3-3) This signal
b
with TXOd
TXLED
g
)
a
TL F 11719– 6
TL F 11719– 7
in a con-
COLED
g
)