sp3508 Exar Corporation, sp3508 Datasheet - Page 22

• Manufacturer Part Number: sp3508
• Description: Rugged 3.3v, 20mbps, 8 Channel Multiprotocol Tranciever With Programmable Dce/dte And Terminination Resistors
• Manufacturer: Exar Corporation

The SP3508 contains highly integrated serial
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 micropro-
cessor control.
The SP3508 has eight drivers, eight receivers,
and Sipex'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.
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 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 accom-
modate the selected interface mode. As the
mode of the drivers is changed, the electrical
characteristics will change to support the re-
quired signal levels. The mode of each driver in
the different interface modes that can be se-
lected is shown in Table 1.
Date: 10/29/04
SP3508 Enhanced WAN Multi–Mode Serial Transceiver
22
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 gener-
ate the RS-232 output rails, the driver outputs
will never exceed +10V. The V.28 driver archi-
tecture 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
V
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 driver can transmit over 120Kbps if neces-
sary.
The third type of drivers are V.11 (RS-422)
differential drivers. Due to the nature of differ-
ential 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 out-
put levels with a load of 100Ω. The strength
allows the SP3508 differential driver to drive
over long cable lengths with minimal signal
degradation. 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. Sipex's new driver design over its prede-
cessors allow the SP3508 to operate over 20Mbps
for differential transmission.
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measurements of +4.0V to +6.0V. When
© Copyright 2004 Sipex Corporation
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