AM79C973BKC\W AMD (ADVANCED MICRO DEVICES), AM79C973BKC\W Datasheet - Page 72

• Manufacturer Part Number: AM79C973BKC\W
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C973BKC\W

• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (min): 3/3.135V
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 160
• Lead Free Status / RoHS Status: Not Compliant

See ANSI/IEEE Std 802.3-1993 Edition, 4.2.3.2.1:
Note: It is possible for the PLS carrier sense indication
to fail to be asserted during a collision on the media. If
the deference process simply times the inter-Frame
gap based on this indication, it is possible for a short
interFrame gap to be generated, leading to a potential
reception failure of a subsequent frame. To enhance
system robustness, the following optional measures,
as specified in 4.2.8, are recommended when Inter-
Frame-SpacingPart1 is other than 0:
1. Upon completing a transmission, start timing the in-
2. When timing an inter-frame gap following reception,
The MAC engine implements the optional receive two
part deferral algorithm, with an InterFrameSpacing-
Part1 time of 6.0 ms. The InterFrameSpacingPart 2 in-
terval is, therefore, 3.4 ms.
The Am79C973/Am79C975 controller will perform the
two-part deferral algorithm as specified in Section 4.2.8
(Process Deference). The Inter Packet Gap (IPG) timer
will start timing the 9.6 ms InterFrameSpacing after the
receive carrier is deasserted. During the first part de-
fe r r a l ( I n t e r Fr a m e S p a c i n g Pa r t 1 - I F S 1 ) , t h e
Am79C973/Am79C975 controller will defer any pend-
ing transmit frame and respond to the receive mes-
sage. The IPG counter will be cleared to 0 continuously
until the carrier deasserts, at which point the IPG
counter will resume the 9.6 ms count once again. Once
the IFS1 period of 6.0 ms has elapsed, the Am79C973/
Am79C975 controller will begin timing the second part
deferral (InterFrameSpacingPart2 - IFS2) of 3.4 ms.
Once IFS1 has completed and IFS2 has commenced,
the Am79C973/Am79C975 controller will not defer to a
receive frame if a transmit frame is pending. This
means that the Am79C973/Am79C975 controller will
not attempt to receive the receive frame, since it will
start to transmit and generate a collision at 9.6 ms. The
Am79C973/Am79C975 controller will complete the
preamble (64-bit) and jam (32-bit) sequence before
ceasing transmission and invoking the random backoff
algorithm.
The Am79C973/Am79C975 controller allows the user
to program the IPG and the first part deferral (Inter-
Frame-SpacingPart1 - IFS1) through CSR125. By
changing the IPG default value of 96 bit times (60h), the
user can adjust the fairness or aggressiveness of the
Am79C973/Am79C975 MAC on the network. By pro-
gramming a lower number of bit times than the ISO/IEC
72
terrupted gap, as soon as transmitting and carrier
sense are both false.
reset the inter-frame gap timing if carrier sense be-
comes true during the first 2/3 of the inter-frame gap
timing interval. During the final 1/3 of the interval,
the timer shall not be reset to ensure fair access to
the medium. An initial period shorter than 2/3 of the
interval is permissible including 0.
P R E L I M I N A R Y
Am79C973/Am79C975
8802-3 standard requires, the Am79C973/Am79C975
MAC engine will become more aggressive on the net-
work. This aggressive nature will give rise to the
Am79C973/Am79C975 controller possibly capturing
the network at times by forcing other less aggressive
compliant nodes to defer. By programming a larger
number of bit times, the Am79C973/Am79C975 MAC
will become less aggressive on the network and may
defer more often than normal. The performance of the
Am79C973/Am79C975 controller may decrease as the
IPG value is increased from the default value, but the
resulting behavior may improve network performance
by reducing collisions. The Am79C973/Am79C975
controller uses the same IPG for back-to-back trans-
mits and receive-to-transmit accesses. Changing IFS1
will alter the per iod for which the Am79C973/
Am79C975 MAC engine will defer to incoming receive
frames.
CAUTION: Care must be exercised when altering
these parameters. Adverse network activity could
result!
This transmit two-part deferral algorithm is imple-
mented as an option which can be disabled using the
DXMT2PD bit in CSR3. The IFS1 programming will
have no effect when DXMT2PD is set to 1, but the IPG
programming value is still valid. Two part deferral after
transmission is useful for ensuring that severe IPG
shrinkage cannot occur in specific circumstances,
causing a transmit message to follow a receive mes-
sage so closely as to make them indistinguishable.
During the time period immediately after a transmission
has been completed, the external transceiver should
generate the SQE Test message within 0.6 to 1.6 ms
after the transmission ceases. During the time period in
which the SQE Test message is expected, the
Am79C973/Am79C975 controller will not respond to
receive carrier sense.
See ANSI/IEEE Std 802.3-1993 Edition, 7.2.4.6 (1):
The Am79C973/Am79C975 controller implements a
carrier sense “blinding” period of 4.0 ms length starting
from the deassertion of carrier sense after transmis-
sion. This effectively means that when transmit two part
deferral is enabled (DXMT2PD is cleared), the IFS1
time is from 4 ms to 6 ms after a transmission. How-
“At the conclusion of the output function, the DTE
opens a time window during which it expects to see
the signal_quality_error signal asserted on the
Control In circuit. The time window begins when
the
CARRIER_OFF. If execution of the output function
does not cause CARRIER_ON to occur, no SQE
test occurs in the DTE. The duration of the window
shall be at least 4.0 ms but no more than 8.0 ms.
During the time window the Carrier Sense Function
is inhibited.”
CARRIER_STATUS
becomes