Sharp LC-32SV40U Service Manual page 60

Disables Drivers for Power Savings
Description
The TRS3221E is a single driver, single receiver RS-232 solution operating from a single VCC supply. The
RS-232 pins provide IEC G1000-4-2 ESD protection. The device meets the requirements of TIA/EIA-232-F
and provides the electrical interface between an asynchronous communication controller and the serial-port
connector. The charge pump and four small external capacitors allow operation from a single 3-V to 5.5-V
supply. These devices operate at data signaling rates up to 250 kbit/s and a maximum of 30-V/µs driver
output slew rate.
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.
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