HYC9088A_07 Datasheet, PDF (5/11 Pages) SMSC Corporation – ARCNET Twisted Pair and Coaxial Compatible High Impedance Transceiver HIT

FUNCTIONAL DESCRIPTION
The HYC9088A 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).
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 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
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
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.
Small Coax Network
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.
Combination of Twisted Pair and Coax
Networks
A Two-Port Link is used to combine twisted pair network and a coax network. A Two-Port Link has a coax connector on
one side and two modular jacks on the other and contains the proper impedance-matching circuitry. Refer to Figure 3 for
an illustration of a twisted pair network combined with a coaxial network.
Revision (02-16-07)
Page 5
DATASHEET
SMSC HYC9088A