The SN65C23243 and SN75C23243 consist of two ports, each containing three line drivers and five line
receivers, and a dual charge-pump circuit with ±15-kV ESD protection pin to pin (serial-port connection pins,
including GND). These devices meet the requirements of TIA/EIA-232-F and provide the electrical interface
between an asynchronous communication controller and the serial-port connector. This combination of drivers
and receivers matches that needed for two typical serial ports used in an IBM PC/AT, or compatible. The charge
pump and four small external capacitors allow operation from a single 3-V to 5.5-V supply. In addition, these
devices include an always-active noninverting output (ROUT2\) per port, which allows applications using the ring
indicator to transmit data while the devices are powered down. The 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 either or both serial ports are 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, the driver outputs of its respective port are
disabled. If FORCEOFF\ is set low, both drivers and receivers (except ROUT2\) 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, and should be done when driving
a serial mouse. With auto-powerdown enabled, the RS-232 port is activated automatically when a valid signal
is applied to any respective receiver input. The INV\ output is used to notify the user if an RS-232 signal is present
at any receiver input. INV\ is high (valid data) if any 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. INV\ is low (invalid data) if all receiver input voltages
are 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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