munication software (such as LapLink™). Transmitters

can be paralleled to drive multiple receivers. Figure 1

shows a complete system connection.

When FORCEOFF is driven to ground or when the Auto-

Shutdown Plus circuitry senses that all receiver and

transmitter inputs are inactive for more than 30sec, the

transmitters are disabled and the outputs go into a high-

impedance state. When powered off or shut down, the

outputs can be driven to ±12V. The transmitter inputs

do not have pull-up resistors. Connect unused inputs to

RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic

output levels. The MAX3224E–MAX3227E feature

inverting outputs that always remain active (Table 1).

The MAX3244E/MAX3245E have inverting three-state

±15kV ESD-Protected, 1µA, 1Mbps, 3.0V to 5.5V,

RS-232 Transceivers with AutoShutdown Plus

8

_______________________________________________________________________________________

MAX3244E

MAX3245E

I/O

CHIP

WITH

UART

CPU

RS-232

POWER-

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

FORCEOFF

FORCEON

INVALID

Figure 1. Interface Under Control of PMU

MAX3244E

MAX3245E

T1OUT

R2OUTB

Tx

5k

UART

T1IN

THREE-STATED

LOGIC

TRANSITION

DETECTOR

R2IN

PROTECTION

DIODE

R2OUT

FORCEOFF = GND

TO

µP

Rx

PREVIOUS

RS-232

Tx

UART

SHDN = GND

GND

Rx

5k

RECEIVER OUTPUT IN SHUTDOWN.

EXTERNAL DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT

PATH THROUGH THE UART'S PROTECTION DIODE.

GND

PROTECTION

DIODE

I

I

Figure 2. The MAX3244E/MAX3245E detect RS-232 activity

when the UART and interface are shut down.