SP508E Datasheet, PDF (20/29 Pages) Exar Corporation – Rugged 20Mbps, 8 Channel Multi-Protocol Transceiver with Programmable DCE/DTE and Termination Resistors

The SP508E contains highly integrated serial
transceivers that offer programmability
between interface modes through software
control. The SP508E offers the hardware
interface modes for RS-232 (V.28), RS-449/
V.36 (V.11 and V.10), EIA-530 (V.11 and V.10),
EIA-530A (V.11 and V.10), V.35 (V.35 and V.28)
and X.21(V.11). The interface mode selection
is done via three control pins, which can be
latched via microprocessor control.
The SP508E has eight drivers, eight receivers,
and Exar's patented on-board charge pump
(5,306,954) that is ideally suited for wide area
network connectivity and other multi-protocol
applications. Other features include digital and
line loopback modes, individual enable/disable
control lines for each driver and receiver, fail-
safe when inputs are either open or shorted,
individual termination resistor ground paths,
separate driver and receiver ground outputs,
enhanced ESD protection on driver outputs
and receiver inputs.
THEORY OF OPERATION
The SP508E device is made up of 1) the drivers,
2) the receivers, 3) a charge pump, 4) DTE/DCE
switching algorithm, and 5) control logic.
Drivers
The SP508E has eight enhanced independent
drivers. Control for the mode selection is done
via a three-bit control word into D0, D1, and
D2. The drivers are prearranged such that for
each mode of operation, the relative position
and functionality of the drivers are set up to
accommodate the selected interface mode.
As the mode of the drivers is changed, the
electrical characteristics will change to support
the required signal levels. The mode of each
driver in the different interface modes that can
be selected is shown in Table 1.
FEATURES
There are four basic types of driver circuits –
ITU-T-V.28 (RS-232), ITU-T-V.10 (RS-423),
ITU-T-V.11 (RS-422), and CCITT-V.35.
The V.28 (RS-232) drivers output single-
ended signals with a minimum of +5V (with
3kΩ & 2500pF loading), and can operate over
120kbps. Since the SP508E uses a charge
pump to generate the RS-232 output rails, the
driver outputs will never exceed +10V. The V.28
driver architecture is similar to Exar's standard
line of RS-232 transceivers.
The RS-423 (V.10) drivers are also single-
ended signals which produce open circuit V_OL
and V_OH measurements of +4.0V to +6.0V.
When terminated with a 450Ω load to ground,
the driver output will not deviate more than 10%
of the open circuit value. This is in compliance
of the ITU V.10 specification. The V.10 (RS-423)
drivers are used in RS-449/V.36, EIA-530, and
EIA-530A modes as Category II signals from
each of their corresponding specifications.
The V.10 drivers are guaranteed to transmit
over 120kbps, but can operate at over 1Mbps
if necessary.
The third type of drivers are V.11(RS-422)
differential drivers. Due to the nature of
differential signaling, the drivers are more
immune to noise as opposed to single-ended
transmission methods. The advantage is
evident over high speeds and long transmission
lines. The strength of the driver outputs can
produce differential signals that can maintain
+2V differential output levels with a load of
100Ω. The signal levels and drive capability of
these drivers allow the drivers to also support
RS-485 requirements of +1.5V differential
output levels with a 54Ω load. The strength
allows the SP508E differential driver to drive
over long cable lengths with minimal signal
degradation. The V.11drivers are used in
RS-449, EIA-530, EIA-530A and V.36 modes
as Category I signals which are used for clock
and data. Exar's new driver design over its
predecessors allow the SP508E to operate
over 20Mbps for differential transmission.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.comSP508E_100_072412
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