73

Corporation

SIGNAL PROCESSING EXCELLENCE

GND

SUPPLY

+5V +12V –12V

SELECT

A

B

SP303

28

1

15

23

6

24

5

20

9

19

10

26

3

27

2

17

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Figure 1. RS232 Operating Mode

to offer more flexible interface capabilities with-

out additional material costs.

The SP303 is available in a 28–pin SOIC pack-

age for operation over the commercial tempera-

ture range.

APPLICATION EXAMPLE

RS-232 MODE SERIAL INTERFACE

Figure 3 shows the SP303CT used in a dual

serial port application which allows both

RS-232 and Macintosh™ AppleTalk™ Mode

interfaces. With SEL A and SEL B low, the port

can be configured for RS-232. In this mode, the

SP303CT is set up for 4 drivers and 4 receivers.

The transmitter enable pin (pin22) has no effect

in this mode.

The RFI filters shown are optional depending

upon the FCC requirements of the system. The

SP303CT has internal slew rate limiting, which

keeps the RS-232 slew rate <30V/

µs. Since the

Figure 2. Macintosh™ AppleTalk™ Operating Mode

differential, while the handshake-out and hand-

shake-in signals are single–ended. The SP303

does not have the extra GPI (General Purpose

Input). All drivers and receivers can operate at

data rates up to 1 Mbps. The differential driver

used for transmitting data signals is equipped

with a tri-state function. When the TxEN pin is

brought low, the differential driver is enabled;

when it is high, the driver outputs are tri–stated.

The tri–state function does not affect any other

driver in either mode of operation.

One SP303 can significantly reduce the board

space necessary for a similar discrete solution

offering both RS-232 and AppleTalk interfaces.

Due to the space savings, the SP303 can provide

multi-mode interfacing to equipment such as

printers or modems without sacrificing addi-

tional board space or cost. This allows the OEM

GND

SUPPLY

+5V +12V –12V

SP303

28

1

15

23

5

6

20

9

10

26

3

2

17

12

14

7

8

SELECT A

SELECT B

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