MAX3221 データシートの表示（PDF） - Maxim Integrated
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MAX3221 Datasheet PDF : 17 Pages
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MAX3221/MAX3223/MAX3243
+3V to +5.5V RS-232 Transceivers
with AutoShutdown
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
MAX3243
I/O
CPU
CHIP
WITH
UART
VCC
RS-232
PROTECTION
DIODE
VCC
Rx
I
UART
Tx
GND
SHDN = GND
PREVIOUS
RS-232
5kΩ
(a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
Figure 1. Interface Under Control of PMU
RS-232 Receivers
The MAX3221/MAX3223/MAX3243’s receivers convert
RS-232 signals to CMOS-logic output levels. All
receivers have one inverting three-state output. In shut-
down (FORCEOFF = low) or in AutoShutdown, the
MAX3221/MAX3223’s receivers are active (Table 1).
Driving EN high places the receiver(s) in a high-imped-
ance state. The MAX3243’s receivers are high imped-
ance when the part is shut down.
The MAX3243 has an always-active complementary
output (R2OUTB). R2OUTB is an extra output that mon-
itors 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 VCC is
set to 0V in shutdown to accommodate peripherals,
such as UARTs (Figure 2).
VCC
TO LOGIC
μP TRANSITION
DETECTOR
PROTECTION
DIODE
I
R2OUTB
VCC
Rx
UART
R2OUT
THREE-STATED
Tx
GND
T1IN
FORCEOFF = GND
MAX3243
R2IN
5kΩ
T1OUT
(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.
Figure 2. The MAX3243 detects RS-232 activity when the
UART and interface are shut down.
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