75

Corporation

SIGNAL PROCESSING EXCELLENCE

Figure 4. Macintosh™ AppleTalk™ Interface.

the transmit data driver in ApppleTalk™ mode.

Both differential drivers have output signals on

each pin that typically swing

±6V. The peak to

peak differential voltage swing is typically

±12V.

The second driver is used for transmitting the

handshake output signal and can be used as

either a differential driver or single ended. This

particular application required a single–ended

inverting signal for the handshake output signal.

Some Macintosh equipment requires an extra

single–ended inverting receiver which is called

a general purpose input. The GPI receiver is

normally connected to pin 7 on the external 8 pin

connector. This receiver is not available on the

SP303CT.

Since the SP303CT is usually connected to the

outside world, it is suggested that the user place

transient voltage suppression devices on each of

the 1/0 lines to ensure up to

±25kV ESD protec-

tion.

TXD

RTS

RXD

CTS

DTR

RFI FILTER

TXDA–

TXDA+

RXDA+

RXDA–

HSKiA

HSKoA

3

4

5

87

6

1

2

GND

SUPPLY

+5V +12V –12V

VCCVDDVEE

SP303

28

1

15

23

6

5

20

9

10

26

3

2

17

12

14

7

8

SELECT A

SELECT B

13

22

No Connect

RFI FILTER

RFI FILTER

RFI FILTER

RFI FILTER

RFI FILTER

TXD

RTS

RXD

CTS

DTR

RFI FILTER

TXDA–

TXDA+

RXDA+

RXDA–

HSKiA

HSKoA

3

4

5

87

6

1

2

GND

SUPPLY

+5V +12V –12V

VCCVDDVEE

SP303

28

1

15

23

6

5

20

9

10

26

3

2

17

12

14

7

8

SELECT A

SELECT B

13

22

No Connect

RFI FILTER

RFI FILTER

RFI FILTER

RFI FILTER

RFI FILTER

POWER SUPPLY SEQUENCING

There are two requirements for power supply

sequencing for the SP303. The first is that V

DD

is always greater than V

when the part is powered up, V

applied 20ms before V