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Exar Coporation 48720 Kato Road, Fremont CA, 94538 (50) 668-7000 Fax (50) 668-707 www.exar.com
SP506_0_0870
a load of 00. The signal levels and drive
capability of these drivers allow the drivers to
also support RS-485 requirements of ±.5V
minimumdifferentialoutputlevelswitha54
load. The driver is designed to operate over
a common mode range of +2V to -7V, which
follows the RS-485 specification. This also
covers the +7V to -7V common mode range
for V. (RS-422) requirements. The V.
drivers are used in RS-449, EIA-530, EIA-
530A and V.36 modes as Category I signals
which are used for clock and data signals.
V.35 Drivers
The fourth type of driver is the V.35 driver.
These drivers were specifically designed
to comply with the requirements of V.35.
Unique to the industry, the Exar V.35 driver
architecture used in the SP506 does not
needexternalterminationresistorstooperate
and comply with V.35. This simplifies exist-
ing V.35 implementations that use external
termination schemes. The V.35 drivers can
produce +0.55V driver output signals with
minimum deviation (maximum 20%) given
an equivalent load of 00. With the help
of internal resistor networks, the drivers
achieve the 50 to 50 source impedance
and the 35 to 65 short-circuit imped-
ance for V.35. The V.35 driver is disabled
and transparent when the decoder is in all
other modes. All of the differential drivers;
V. (RS-422) and V.35, can operate over
20Mbps.
Driver Enable and Input
AllthedriversintheSP506containindividual
enablelineswhichcantri-statethedriverout-
puts when a logic "" is applied. This simpli-
fieshalf-duplexconfigurationsforsomeappli-
cations and also provides simpler DTE/DCE
flexibility with one integrated circuit.
The driver inputs are both TTL or CMOS
compatible. Each driver input should have a
pull-down or pull-up resistor so that the out-
put will be at a defined state. Unused driver
inputs should not be left floating.
Receivers
The SP506 has seven (7) independent re-
ceivers which can be programmed for the
different interface modes. Control for the
Drivers
The SP506 has seven (7) enhanced in-
dependent drivers. Control for the mode
selection is done via a four–bit control word.
The drivers are prearranged such that for
each mode of operation, the relative posi-
tion and functionality of the drivers are set
up to accommodate the selected interface
mode.As the mode ofthe drivers is changed,
the electrical characteristics will change to
support the requirements of clock, data, and
control line signal levels. Table shows the
mode of each driver in the different interface
modes that can be selected.
There are four basic types of driver circuits
— V.28, V., V.0 and V.35.
V.28 Drivers
TheV.28driversoutputsingle–endedsignals
with a minimum of +5V (with 3k & 2500pF
loading),andcanoperatetoatleast20kbps
under full load. Since the SP506 uses a
charge pump to generate the RS-232 output
rails, the driver outputs will never exceed
+0V. The V.28 drivers are used in RS-232
mode for all signals, and also in V.35 mode
where four (4) drivers are used as the control
line signals (DTR, RTS, LL, and RL).
V.10 Drivers
The V.0 (RS-423) drivers are also single–
endedsignalswhichproduceopencircuitV
OL
and V
OH measurements of +4.0V to +6.0V.
Whenterminatedwitha450loadtoground,
the driver output will not deviate more than
0% of the open circuit value. This is in
compliance of the ITU V.10 specification.
The V.0 drivers are used in RS-449, EIA-
530, EIA-530Aand V.36 modes as Category
II signals from each of their corresponding
specifications.
V.11 Drivers
The third type of driver is a V. (RS-422)
type differential driver. Due to the nature of
differential signaling, the drivers are more
immunetonoiseasopposedtosingle-ended
transmissionmethods. Theadvantageisevi-
dentoverhighspeedsandlongtransmission
lines. The strength of the driver outputs can
producedifferentialsignalsthatcanmaintain
typically +2.2V differential output levels with