5

300

Receivers

The receiver inputs accept up to

±30V while presenting the

required 3k

Ω to 7kΩ input impedance even it the power is off

1.3V which is within the

±3V limits, known as the transition

region, of the RS-232 specification. The receiver output is

greater than 2.4V and high whenever the input is floating or

driven between +0.8V and -30V. The receivers feature 0.5V

hysteresis to improve noise rejection.

Applications

The ICL232 may be used for all RS-232 data terminal and

communication links. It is particularly useful in applications

where

±12V power supplies are not available for conven-

tional RS-232 interface circuits. The applications presented

represent typical interface configurations.

A simple duplex RS-232 port with CTS/RTS handshaking is

illustrated in Figure 10. Fixed output signals such as DTR

(data terminal ready) and DSRS (data signaling rate select)

is generated by driving them through a 5k

Ω resistor

connected to V+.

In applications requiring four RS-232 inputs and outputs

(Figure 11), note that each circuit requires two charge pump

capacitors (C1 and C2) but can share common reservoir

capacitors (C3 and C4). The benefit of sharing common res-

ervoir capacitors is the elimination of two capacitors and the

reduction of the charge pump source impedance which

effectively increases the output swing of the transmitters.

300

Ω

400k

Ω

V-

V+

FIGURE 7. TRANSMITTER

5k

Ω

GND

FIGURE 8. RECEIVER

Average Propagation Delay =

2

OR

OR

FIGURE 9. PROPAGATION DELAY DEFINITION

-

+

-

+

-

+

CTR (20) DATA

TERMINAL READY

DSRS (24) DATA

SIGNALING RATE

RS-232

INPUTS AND OUTPUTS

TD (2) TRANSMIT DATA

RTS (4) REQUEST TO SEND

RD (3) RECEIVE DATA

CTS (5) CLEAR TO SEND

SIGNAL GROUND (7)

15

8

13

7

14

16

-

+

6

R2

R1

T2

T1

9

12

10

11

4

5

3

1

ICL232

C1

1

µF

C2

1

µF

TD

RTS

RD

CTS

SELECT

+5V

INPUTS

OUTPUTS

TTL/CMOS

C3

1

µF

C4

1

µF

2

5k

Ω

5k

Ω

FIGURE 10. SIMPLE DUPLEX RS-232 PORT WITH CTS/RTS

HANDSHAKING

ICL232