AM79C100JC datasheet(9/24 Pages) AMD

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Am79C100

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

± 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 AV

DD, 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

± 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

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