Corporation

SIGNAL PROCESSING EXCELLENCE

72

Pin 26 — R

UART.

Pin 27 — N.C. — No Connection.

Pin 28 — V

PIN ASSIGNMENTS — MACINTOSH™

APPLETALK™ MODE

Pin 1 — V

Pin 2 — R

UART’s RxD (non–inverted); V

V

Pin 3 — R

UART’s RxD (inverted); V

IH

= 0.2V;

V

Pin 4 — N.C. — No Connection.

Pin 5 — T

UART’s TxD (non–inverted); tri–stated when

UART’s RTS is not asserted; V

V

Pin 6 — T

UART’s TxD (inverted); tri–stated when RTS

is not asserted; V

min R

Pin 7 — SEL A — Select A; used with Select B

(pin 8) to select operating mode. Logic “0” on

both SEL A and SEL B selects RS-232 mode;

logic “1” on both SEL A and SEL B selects

AppleTalk™ mode.

Pin 8 — SEL B — Select B; used with Select A

(pin 7) to select operating mode. Logic “0” on

both SEL A and SEL B selects RS-232 mode;

logic “1” on both SEL A and SEL B selects

AppleTalk™ mode.

Pin 9— T

from UART’s DTR (inverted) ;V

V

Pin 10 — T

from UART’s DTR (non–inverted); V

min; V

Pin 11 — N.C. — No Connection.

Pin 12— R

clock; received non–inverted at UART’s CTS

and TRxC; V

minimum.

Pin 13 — N.C. — No Connection.

Pin 14 — GND — Signal ground. Connected to

logic and chasis ground.

Pin 15 — V

Pin 16 — N.C. — No Connection.

Pin 17 — R

put; connects to UART’s CTS and TRxC.

Pin 18 — N.C. — No Connection.

Pin 19 — T

mode.

Pin 20 — T

connects to UART’s DTR output.

Pin 21 — N.C. — No Connection.

Pin 22 — TxEN — Transmit data driver enable;

connects to UART’s RTS; transmit data driver

is enabled when this pin is low.

Pin 23 — T

nects to UART’s TxD output.

Pin 24 — N.C. — No Connection.

Pin 25 — N.C. — No Connection.

Pin 26 — R

connects to UART’s RxD input.

Pin 27 — N.C. — No Connection.

Pin 28 — V

FEATURES…

The SP303 is a single chip device that offers

both RS-232 and AppleTalk interfaces. When

configured for RS-232 mode, the SP303 pro-

vides 4 drivers and 4 receivers. When the part is

programmed for AppleTalk mode, the SP303

supports Macintosh–type ports. The mode can

be changed at any time by bringing both the SEL

A and the SEL B pins high for Mac mode, or low

for RS-232 mode.

The RS-232 line driver circuits convert TTL–

logic level inputs into inverted RS-232 output

signals. The RS-232 receivers convert the EIA

RS-232 input signals to inverted TTL output

logic levels. The receivers have voltage hyster-

esis, which helps eliminate spurious output tran-

sitions that might result from low–amplitude

noise voltages during slower-speed signal tran-

sitions.

When the SP303 is programmed for Mac mode,

the transmit data and receive data signals are