Sharp LC-32LE440U, Service Manual

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· Operates With 3-V to 5.5-V VCC Supply
· Operates up to 250 kbit/s
· One Driver and One Receiver
· Low Standby Current . . . 1 µA Typical
· External Capacitors . . . 4 ´ 0.1 µF
· Accepts 5-V Logic Input With 3.3-V Supply
· Alternative High-Speed Pin-Compatible (1 Mbit/s)
.TRSF3221E
· Auto-Powerdown Feature Automatically
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.