SP3508EB Datasheet, PDF (25/36 Pages) Sipex Corporation – Evaluation Board Manual

The SP3508 contains highly integrated se-
rial transceivers that offer programmability
between interface modes through software
control. The SP3508 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 SP3508 has eight drivers, eight receiv-
ers, and a 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.
THEORY OF OPERATION
The SP3508 device is made up of
1) the drivers
2) the receivers
3) charge pumps
4) DTE/DCE switching algorithm
5) control logic.
Drivers
The SP3508 has eight enhanced indepen-
dent 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 driv-
ers 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 dif-
ferent 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 SP3508 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 Sipex'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 com-
pliance 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 driver can transmit
over 120Kbps if necessary.
The third type of drivers are V.11 (RS-422)
differential drivers. Due to the nature of dif-
ferential signaling, the drivers are more im-
mune to noise as opposed to single-ended
transmission methods. The advantage is
evident over high speeds and long trans-
mission lines. The strength of the driver
outputs can produce differential signals that
can maintain +2V differential output levels
with a load of 100Ω. The strength allows the
SP3508 differential driver to drive over long
cable lengths with minimal signal degrada-
tion. The V.11 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. Exar's new driver design over its
predecessors allow the SP3508 to operate
over 20Mbps for differential transmission.
The fourth type of drivers are V.35 differential
drivers. There are only three available on the
SP3508 for data and clock (TxD, TxCE, and
TxC in DCE mode).
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com
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