5

SP495

Quad Differential RS-485 Transceiver

© Copyright 2000 Sipex Corporation

+3V

0V

RE

5V

R

0V

1.5V

1.5V

R

1.5V

1.5V

0.5V

0.5V

Output normally LOW

Output normally HIGH

Figure 9. Receiver Enable and Disable Times

DESCRIPTION

General Description...

The SP495 is a quad differential transceiver that

meets the requirements of RS-485, RS-422, and

differential SCSI at data rates to beyond 10Mbps.

Fabricated with a proprietary Sipex BiCMOS

process, the SP495 requires only a fraction of the

power of older bipolar designs.

The SP495 features three half-duplex transceivers

suitable for data bus connections and a fourth

full-duplex transceiver with independent enables

ideal for use as a control bus transceiver. A

complete SCSI initiator or target interface can be

implemented using five SP495s.

The RS-485 standard is ideal for multi-drop

applications and for long-distance interfaces.

RS-485 allows up to 32 drivers and 32 receivers

to be connected to a single data bus, making it an

ideal choice for multi-drop applications. Since

the cabling can be as long as 4,000 feet, RS-485

transceivers are specified for operation with a

wide (-7V to +12V) common mode range to

accommodate ground potential differences.

Because RS-485 is a low impedance differential

interface, data is virtually immune to noise in the

transmission line.

Drivers...

The differential drivers for the SP495 have typical

output voltage swings (no load) of 0 to +5Volts.

With loading to the RS-485 specification (54

Ω),

drivers must maintain outputs greater than 1.5V.

The three half-duplex drivers of the SP495 have

independent Driver Enable control lines which

are active HIGH. A logic HIGH on DEx (pins 1,

4, or 5 of the SP495) will enable the addressed

differential driver output. A logic LOW on DEx

will tri-state the driver output and enable the

receiver. The fourth driver is controlled by its

own DE4 Enable line and can be used in half -

duplex or full-duplex modes.

Receivers...

The differential receivers for the SP495 have an

input sensitivity of

±200mV. Input impedance is

typically 15k

Ω (12kΩ minimum). A wide

common mode range of -7V to +12V allows for

large ground potential differences between widely

separated systems. These receivers are equipped

with a fail-safe feature which guarantees that the

receiver output will be in a HIGH state when the

input is left unconnected (note: this feature

operates with floating inputs, not terminated

inputs).

Like the half-duplex drivers, the three half-duplex

receivers of the SP495 have independent Re-

ceiver Enable control lines which are active

LOW. A logic LOW on REx (pins 1, 4, or 5 of

the SP495) enables the differential receivers. A

logic HIGH on REx tri-states the receivers. The

fourth receiver is controlled by its own RE4

Enable line and can be used in half-duplex or

full-duplex modes.