Datasheet
±
SLLS348M − JUNE 1999 − REVISED MARCH 2004
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
description/ordering information (continued)
Flexible control options for power management are available when the serial port is inactive. The
auto-powerdown feature functions when FORCEON is low and FORCEOFF
is high. During this mode of
operation, if the device does not sense a valid RS-232 signal on the receiver input, the driver output is disabled.
If FORCEOFF
is set low and EN is high, both the driver and receiver are shut off, and the supply current is
reduced to 1 µA. Disconnecting the serial port or turning off the peripheral drivers causes the auto-powerdown
condition to occur. Auto-powerdown can be disabled when FORCEON and FORCEOFF
are high. With
auto-powerdown enabled, the device is activated automatically when a valid signal is applied to the receiver
input. The INVALID
output notifies the user if an RS-232 signal is present at the receiver input. INVALID is high
(valid data) if the receiver input voltage is greater than 2.7 V or less than −2.7 V, or has been between −0.3 V
and 0.3 V for less than 30 µs. INVALID
is low (invalid data) if the receiver input voltage is between −0.3 V and
0.3 V for more than 30 µs. Refer to Figure 5 for receiver input levels.
Function Tables
EACH DRIVER
INPUTS
OUTPUT
DIN FORCEON FORCEOFF
VALID RIN
RS-232 LEVEL
OUTPUT
DOUT
DRIVER STATUS
X X L X Z Powered off
L H H X H
Normal operation with
H HH XL
Normal operation with
auto-powerdown disabled
L L H Yes H
Normal operation with
H LH YesL
Normal operation with
auto-powerdown enabled
L L H No Z
Powered off by
H L H No Z
Powered off by
auto-powerdown feature
H = high level, L = low level, X = irrelevant, Z = high impedance
EACH RECEIVER
INPUTS
OUTPUT
RIN EN
VALID RIN
RS-232 LEVEL
OUTPUT
ROUT
L L X H
H LX L
X HX Z
Open L No H
H = high level, L = low level, X = irrelevant,
Z = high impedance (off), Open = disconnected
input or connected driver off