AM79C100 Ver la hoja de datos (PDF) - Advanced Micro Devices
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AM79C100 Datasheet PDF : 24 Pages
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Signal Quality Error (SQE) Test (Heartbeat)
Function
When the SQE TEST pin is driven LOW, TPEX Plus will
routinely exercise the collision detection circuitry by
generating an SQE Test message at the end of every
transmission. This signal is a self-test indication to the
DTE that the MAU collision circuitry is functional and
the AUI cable/connection is intact. An SQE Test mes-
sage consists of a 10 MHz signal on the CI± pair with a
duration of 5 to 15 bit times (500 ns to 1500 ns). When
enabled, an SQE Test will occur at the end of every
transmission, starting 6 to 16 bit times (600 ns to
1600 ns) after the last transition of the transmitted sig-
nal. For repeater applications, the SQE Test function
can be disabled by tying the SQE TEST pin HIGH or by
leaving it disconnected. The COL output will remain in-
active during the SQE Test message on CI±.
Jabber Function
The Jabber function inhibits the twisted-pair transmit
function of TPEX Plus if the DO± circuit is active for an
excessive period (20 ms to 150 ms). This prevents any
one node from disrupting the network due to a
“stuck on” or faulty transmitter. If this maximum trans-
mit time is exceeded, the TPEX Plus transmitter cir-
cuitry is disabled and a 10 MHz signal is driven onto the
CI± pair. Once the transmit data stream is removed
from the DO± input pair, an “unjab” time of 250 ms to
750 ms will elapse before the TPEX Plus removes the
10 MHz signal from the CI± pair and re-enables the
transmit circuitry.
When jabber is detected, TPEX Plus will activate the
COL driver, disable the XMT driver (regardless of DO±
activity), and allow the RCV driver to indicate the
current state of the RXD± pair. If there is no receive ac-
tivity on RXD±, only COL will be active during Jabber
Detect. If there is RXD± activity, both COL and RCV will
be active.
Power Down
In addition to on-board power-on-reset circuitry, the
PRDN/RST pin is used as the master reset for TPEX
Plus. PRDN/RST must be driven LOW for a minimum
of 2 µs for reset to occur. The PRDN/RST pin can also
be used to put the TPEX Plus into an inactive or “sleep”
state, causing the device to consume less power. This
feature is useful in battery-powered or low-duty-cycle
systems. Driving PRDN/RST LOW resets the internal
logic of TPEX Plus and places the device into idle
mode. In this mode, the twisted-pair driver pins (TXD±,
TXP±) are driven LOW, the AUI pins (CI±, DI±) are
pulled to AVDD, the LNKST and RXPOL pins are in the
inactive state, and the XMT, RCV, and COL pins are in
the high-impedance state. TPEX Plus will remain in idle
mode as long as PRDN/RST is asserted.
Following the rising edge of the signal on PRDN/RST,
TPEX Plus will remain in the reset state for up to 10 µs.
Immediately after the reset condition is removed, TPEX
Plus will drive the XMT, RCV, and COL outputs LOW for
20 ms to 62 ms as a lamp test feature, and will be
forced into the Link Fail state. TPEX Plus will move to
the Link Pass state only after 5 to 6 link beat pulses
and/or a single received message is detected on the
RXD± pair.
Test Modes
TPEX Plus implements two types of loopback test
modes suitable for Station (DTE) or Repeater applica-
tions. The test mode is entered by driving the TEST1
pin HIGH. The TEST2 pin is intended for factory test
only and should be tied HIGH for test mode or normal
operation. The two available test modes are:
1. Station (DTE): SQE TEST pin LOW. Data received
on the DO± input pair is transmitted onto the TXD±
and TXP± output pairs, and data received on the
RXD± input pair is transmitted onto the DI± output
pair.
2. Repeater: SQE TEST pin HIGH. Data received on
the DO± input pair is looped back onto the DI± out-
put pair, and data received on the RXD± pair is
looped back and retransmitted on the twisted-pair
drivers (TXD± and TXP± pairs).
In both modes, TPEX Plus will be forced into the Link
Pass state and will not enter the Link Fail state, regard-
less of RXD± inactivity. The following functions are dis-
abled: jabber circuit, collision detection, and collision
oscillator. The functions that remain enabled are: the
DO± and RXD± squelch circuits, XMT and RCV out-
puts, link beat pulse generation, and polarity detection/
correction. In addition, in both modes, the COL pin (not
used to indicate collision during test modes) will go ac-
tive for the duration of any transmit activity on the
TXD±/TXP± pairs, providing a leading high-to-low edge
indicating the start of packet transmission or link beat
pulse generation.
Upon exiting either of the test modes, the Link Test
State Machine will be forced into the Link Fail state.
RXPOL may be pulled LOW and receive polarity
correction will be disabled.
TPEX Plus External Components
Figure 1 shows a typical twisted-pair port external com-
ponents schematic. The resistors used should have a
±1% tolerance to ensure interoperability with
10BASE-T-compliant networks. The filters and pulse
transformers are necessary devices that have a major
influence on the performance and compliance of a
TPEX Plus-based MAU. Specifically, the transmitted
waveforms are heavily influenced by filter characteris-
tics and the twisted-pair receivers employ several
Am79C100
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