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SP334CT

Programmable RS-232/RS-485 Transceiver

Signal Processing Technologies 

The RS-232 receiver has a single–ended input

with a threshold of 0.8V to 2.4V. The RS-232

receiver has an operating voltage range of ±15V

and can receive signals up to 120kbps. RS-232

receivers are used in RS-232 mode for all signal

types include data, clock, and control lines of

the RS-232 serial port.

The differential RS-485 receiver has an input

impedance of 15kΩ and a differential threshold

of ±200mV. Since the characteristics of an RS-

422 receiver are actually subsets of RS485, the

receivers for RS-422 requirements are identical

to the RS-485 receivers. All of the differential

receivers can receive data up to 10Mbps.

Enable Pins

The SP334 drivers can be enabled by use of the

TXEN pin. A logic HIGH will enable the driver

outputs and a logic LOW will tri-state the

+5V

outputs. The drivers can only be tri-stated in

RS-485 mode. The drivers are always active in

RS-232 mode.

The receiver outputs can also be tri-stated by

use of the RXEN pin. A logic LOW will enable

the receiver outputs and a logic HIGH will

tri-state the outputs. The receiver tri-state

capability is offered for both RS-232 and

RS-485 modes. The input impedance if the

receivers during tri-state is at least 12kΩ.

Applications

The SP334 allows the user flexibility in having

a RS-232 or RS-485 serial port without using

two different discrete active ICs. Figure 18

shows a connection to a standard DB-9 RS-232

connector. In RS-485 mode, the SP334 is a full

duplex transceiver, however, a half duplex

configuration can be made by connecting the

driver outputs to the receiver inputs.

0.1µF

0.1µF

0V

TxD

RTS

DTR

5

9 C1+

VCC

SP334 12 C1-

11 C2+

13

C2-

25

RS232/RS485

0.1µF

V+ 10

V– 14

0.1µF

Vcc

400KΩ

27 TI1

T1

Vcc

400KΩ

28 TI2

T2

Vcc

400KΩ

1 TI3

T3

TX1 6

TX2 7

TX3 4

RxD

19 RX1

CTS

20 RX2

DSR

21 RX3

DCD

22 RX4

RI

23 RX5

GND

8

RI1

R1

5KΩ 15

R2

RI2

5KΩ 16

R3

RI3

5KΩ 17

R4

RI4

5KΩ 18

R5

RI5

5KΩ 24

26

RXEN

1

DCD

DSR

RxD

6

RTS

TxD

CTS

DTR

RI

9

SG

5

Figure 18. SP334 Configuration to a DB-9 Serial Port

SP334DS/10

Programmable RS-232/RS-485 Transceiver

10

© Copyright 2000 Sipex Corporation

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