6

TGoddard/SP333/9617R0

SP333 RS-232/AppleTalk Programmable Transceiver

© Copyright 2000 Sipex Corporation

THEORY OF OPERATION...

The SP333 is a single chip device that can be

configured via software for either RS-232 or

AppleTalk™ interface modes at any time. The

SP333 is made up of three basic circuit ele-

ments: single-ended drivers and receivers, dif-

ferential drivers and receivers, and charge pump.

APPLETALK™ DRIVERS/RECEIVERS...

To program the SP333 for MacMode, Pin 25

should be connected to a logic HIGH.

In

MacMode, the SP333 offers a complete

AppleTalk serial interface.

The driver section of the AppleTalk interface is

made up of a differential driver and a single-

ended inverting driver. The differential driver

has voltage swings that are typically

±5V on

each output pin under loaded conditions, and

typically

±8V under no-load conditions. The

differential driver can maintain

±3.6V (mini-

mum) swings (per pin) under worst case load

conditions of 450

Ω between the differential

output.

The differential driver is equipped with a tri-

state control pin. When TXEN is a logic LOW,

the differential driver is active. When the TXEN

pin is a logic HIGH, the differential driver

outputs are tri-stated.

The TXEN pin only

functions in MacMode.

The differential

AppleTalk driver can support data rates up to

10Mbps.

The single-ended AppleTalk driver also has

typical voltage output swings of

±5V under

loaded conditions, and

±8V under no-load con-

ditions. The single-ended AppleTalk driver can

maintain

±3.6V (minimum) swings under worst

case conditions of 450

Ω to ground. The single-

ended AppleTalk driver can support data rates

over 400kbps.

The receiver section of the SP333 is made up of

a differential receiver, a single-ended non-in-

verting receiver , and a single-ended inverting

receiver. The differential receiver has an input

sensitivity of

±200mV over a common mode

range of

±7V. The receivers have a typical input

resistance of 15k

Ω (12kΩ minimum). The

differential receiver can receive data up to

10Mbps.

The single-ended non-inverting receiver has a

±200mV input threshold, however, the input

voltage can vary between

±7V. The typical

input resistance of the single-ended non-invert-

ing receiver is 15k

Ω (12kΩ minimum). The

single-ended non-inverting receiver can also

receive data up to 10Mbps.

The SP333 also has a single-ended inverting

receiver input. This receiver is basically an RS-

232 receiver (R5 receiver) and is typically used

as a GPI (General Purpose Input) in the

AppleTalk interface. The GPI input has TTL-

compatible input thresholds that can receive

+3V

0V

RXEN

5V

0V

1.5V

1.5V

1.5V

1.5V

0.5V

0.5V

Output normally LOW

Output normally HIGH

Figure 6. Receiver Enable and Disable Times