9

LTC1323

SWITCHI G WAVEFOR S

Figure 12. Single-Ended Receiver

1.5V

RXI, RXI

RXI

RXI

1.5V

V

LTC1323 • F12

0.8V

1.5V

2.4V

1.5V

Figure 13. Receiver Enable and Disable

1.5V

3V

0V

RXEN

1.5V

RXO, RXO, RXDO

5V

0.5V

OUTPUT NORMALLY LOW

0V

LTC1323 • F13

2.3V

2.3V

OUTPUT NORMALLY HIGH

0.5V

RXO, RXO, RXDO

APPLICATIO S I FOR ATIO

Functional Description

The “serial port” on the back of an Apple-compatible

computer or peripheral is a fairly versatile “multi-protocol”

connector. It must be able to connect to a wide bandwidth

LAN (an AppleTalk/LocalTalk network), which requires a

high speed differential transceiver to meet the AppleTalk

specification, and it must also be able to connect directly to

a printer or modem through a short RS232 style link. The

LTC1323 is designed to provide all the functions necessary

to implement such a port on a single chip. Two versions of

the LTC1323 are available: a 16-pin SO version which

provides the minimum solution for interfacing to an

AppleTalk network in a smaller package, and a larger 24-pin

SO Wide version which additionally includes all the hand-

shaking lines required to implement a complete AppleTalk/

modem/printer serial port. All LTC1323s run from a single

5V power supply while providing true single-ended com-

patibility, and include a 0.5

µA low power shutdown mode

to improve lifetime in battery-powered devices. The 24-

pin SO Wide version also includes a receiver keep-alive

mode for monitoring external signals while drawing 65

µA

typically.

The LTC1323 includes an RS422-compatible differential

driver/receiver pair for data transmission, with the driver

specified to drive 2V into the 100

Ω primary of a typical

LocalTalk interface transformer/RFI interference network.

Either output of the differential RS422 driver can also act as

an single-ended driver, allowing the LTC1323 to commu-

nicate over a standard serial connection. The 24-pin SO

Wide LTC1323 also includes an extra single ended only

driver and two extra RS232-compatible single-ended re-

ceivers for handshaking lines. All versions include an on-

board charge pump to provide a regulated – 5V supply

required for the single-ended drivers. The charge pump

can also provide up to 10mA of external load current to

power other circuitry.