Datasheet

RS-232 Receivers
The MAX3221/MAX3223/MAX3243’s receivers convert
RS-232 signals to CMOS-logic output levels. All receiv-
ers have one inverting three-state output. In shutdown
(FORCEOFF = low) or in AutoShutdown, the MAX3221/
MAX3223’s receivers are active (Table 1). Driving EN high
places the receiver(s) in a high-impedance state. The
MAX3243’s receivers are high impedance when the part
is shut down.
The MAX3243 has an always-active complementary
output (R2OUTB). R2OUTB is an extra output that
monitors receiver activity while the other receivers
are high impedance. This allows Ring Indicator to be
monitored without forward biasing other devices
connected to the receiver outputs. This is ideal for
systems where V
CC
is set to 0V in shutdown to
accommodate peripherals, such as UARTs (Figure 2).
Figure 2. The MAX3243 Detects RS-232 Activity When the
UART and Interface Are Shut Down.
Figure 1. Interface Under Control of PMU
MAX3243
I/O
CHIP
WITH
UART
CPU
RS-232
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
MAX3243
T1OUT
R2OUTB
Tx
5kΩ
UART
V
CC
T1IN
THREE-STATED
LOGIC
TRANSITION
DETECTOR
R2IN
PROTECTION
DIODE
R2OUT
FORCEOFF = GND
V
CC
TO
µP
Rx
PREVIOUS
RS-232
Tx
UART
SHDN = GND
V
CC
V
CC
GND
Rx
5kΩ
(a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
(b) NEW MAX3243: IN SHUTDOWN, R2OUTB IS USED TO MONITOR EXTERNAL
DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT PATH
THROUGH THE UART'S PROTECTION DIODE.
GND
PROTECTION
DIODE
I
I
MAX3221/MAX3223/
MAX3243
+3V to +5.5V RS-232
Transceivers with AutoShutdown
www.maximintegrated.com
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