12

LTC1334

S

APPLICATI

I FOR ATIO

Figure 12. Multiprotocol Interface

with Optional, Switchable Terminations

326

25

RX OUT

24

RX OUT

22

DR IN

8

SEL1

23

21

DR IN/ENABLE

LB

5V

LTC1334 • F12

LTC1334

28

C2

C1

2

1

27

4

INPUT A

K1A

K1B

120

Ω

5

INPUT B

6

OUTPUT A

7

OUTPUT B

13

INPUT A

12

INPUT B

11

OUTPUT A

10

14

OUTPUT B

PORT 1

INTERFACE

20

16

ON/OFF

RX OUT

17

RX OUT

19

DR IN

9

SEL2

18

15

DR IN/ENABLE

PORT 2

INTERFACE

AROMAT CORP (800) 276-6289

ZETEX (516) 543-7100

*

**

0.1

µF

0.1

µF

0.1

µF

0.1

µF

0.1

µF

120

Ω

K2A

120

Ω

K2B

120

Ω

TERM1

360k

FMMT619**

K1*

TX2A-5V

7.5k

TERM2

360k

FMMT619**

K2*

TX2A-5V

7.5k

5V

5V

Figure 13. Typical Connection for RS232/EIA562 Interface

1/2 LTC1334

1/2 LTC1334

LTC1334 • F13

19

18

17

16

9

DR IN

DR IN

RX OUT

RX OUT

4

5

6

7

11

10

13

12

24

25

22

23

8

RX OUT

RX OUT

DR IN

DR IN

RS232/

EIA562

INTERFACE

LINES

Each receiver in the LTC1334 is designed to present one

unit load (5k

Ω nominal for RS232 and 12kΩ minimum for

RS485) to the cable. Some RS485 and RS422 applications

call for terminations, but these are only necessary at two

nodes in the system and they must be disconnected when

operating in the RS232 mode. A relay is the simplest, low-

est cost method of switching terminations. In Figure 12

TERM1 and TERM2 select 120

Ω terminations as needed.

If terminations are needed in all RS485/RS422 applica-

tions, no extra control signals are required; simply con-

nect TERM1 and TERM2 to SEL1 and SEL2.

Typical Applications

A typical RS232/EIA562 interface application is shown in

Figure 13 with the LTC1334.

A typical connection for a RS485 transceiver is shown in

Figure 14. A twisted pair of wires connects up to 32 drivers

and receivers for half duplex multipoint data transmission.

The wires must be terminated at both ends with resistors

equal to the wire’s characteristic impedance. An optional

shield around the twisted pair helps to reduce unwanted

noise and should be connected to ground at only one end.

Figure 14. Typical Connection for RS485 Interface

5V

4

1/2 LTC1334

1/2

LTC1334

1/2 LTC1334

LTC1334 F14

RX OUT

DR ENABLE

DR IN

5V

120

Ω

5

6

7

24

23

22

8

13

12

11

10

9

RX OUT

18

5V

DR ENABLE

76

54

22

DR IN

RX OUT

DR ENABLE

23

24 8

17

DR IN

19

120

Ω