HYC9088A Datasheet, PDF (5/13 Pages) SMSC Corporation – ARCNET TWISTED PAIR AND COAXIAL COMPLATIBLE HIGH IMPEDANCE TRANSCEIVER HIT

FUNCTIONAL DESCRIPTION
The HIT integrates a host of discrete components
into a hybrid module and provides the Local Area
Network designer with space and cost savings as
well as the enhanced reliability of a single
component. Since the HIT is a high impedance
transceiver, it does not disturb the characteristic
impedance of the cable used to interconnect
ARCNET nodes. The two far ends of the twisted
pair cable must be terminated using terminating
resistors equal to the characteristic impedance of
the cable. The HIT is made up of a transmit
section and a receive section. (Please refer to
Figure 1).
16 Volts peak-to-peak. The exact output voltage of
the HIT will vary depending on the characteristic
impedance of the cable used. The driving circuitry
of the HIT has been designed to present a high
impedance on the cable in order to minimize
loading.
The DISABLE input of the HYC9088 can be used
to prevent the device from transmitting. During
normal operation, the DISABLE input is tied to
ground.
Receiver Section
Transmit Section
The ARCNET LAN controller transmits a logic "1"
by generating two 100 ns non-overlapping
negative pulses, nPULSE1 and nPULSE2. These
signals are converted by the HIT into a 200 ns
dipulse signal. The HIT shapes the 200 ns signal
into a single cycle of a 5 MHz sine-wave and filters
higher frequency components. The dipulse signal
is then transformer-coupled onto the cable and
has a minimum voltage output of
The received dipulse signal from the cable is
electrically isolated through the use of a
transformer. This signal is passed through a filter
which eliminates out of band noise. The receive
signal is then fed to a comparator which converts it
into a TTL signal ready to be applied to the LAN
controller chip. The comparator compares the
received signal to an internal voltage threshold to
distinguish noise from real signal.
APPLICATION INFORMATION
Small Twisted Pair Networks
Small Coax Network
The HIT eliminates the need for active hubs in
small ARCNET networks. For example, a ten
node ARCNET network can be constructed by
connecting ten HITs using a daisy-chained or bus
configuration (see Figure 2). Note that both
extremes of the cable must be terminated with a
resistor which matches the characteristic
impedence of the Twisted Pair Cable. For the
cable types specified in Table 1, the maximum
length of the twisted pair cable recommended is
400 feet.
No active hub is required for an ARCNET network
consisting of eight nodes or less using the
HYC9088 for coax cable (See Figure 2A). Both
ends of the cable must be terminated with a
resistor which matches the characteristic
impedance of the coax cable. For the RG62 cable
specified in Table 1, the maximum length of the
coax cable recommended is 1000 feet.
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