SP334DS/10

Programmable RS-232/RS-485 Transceiver

© Copyright 2000 Sipex Corporation

10

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 12k

Ω.

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.

25

12

14

+5V

GND

CTS

TxD

RTS

0.1

µF

0.1

µF

VCC

V+

V–

DTR

RxD

T1

T2

T3

R1

TX1

TX2

TX3

RI1

TI1

TI2

TI3

RX1

RX5

RX4

RX3

RX2

RI5

RI4

RI3

RI2

19

15

4

5

6

7

8

10

0.1

µF

0.1

µF

C1+

C1-

C2+

C2-

9

11

13

23

22

21

20

16

RS232/RS485

27

28

1

400K

Ω

Vcc

400K

Ω

Vcc

400K

Ω

Vcc

0V

DSR

DCD

RI

17

18

24

5K

Ω

5K

Ω

5K

Ω

5K

Ω

SP334

R2

R3

5K

Ω

R4

R5

RXEN

26

1

9

5

6

TxD

DTR

RTS

RxD

CTS

DSR

DCD

RI

SG

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

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 15k

Ω 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