Below is the cabling diagram for connecting a Merlin-Gerin ES-4 ("Pulsar") UPS to a
standard RS-232 serial port in a computer running Windows NT (3.5 and higher) and the
native UPS service provided with the base installation of the OS.
You'll be needing two 4,7kOhm 1/4 Watt resistors, wire, and the appropriate connectors
(one male DB9 and one female DB9 or DB25, according to your configuration).
You have to modify BOOT.INI in order to pass the appropriate boot parameter to the
NT kernel to prevent it from resetting the serial port where the UPS is connected,
otherwise toggling DTR seems not a good idea ;-)
The BOOT.INI parameter is /NoSerialMice:COM2 (or whatever), to be put in the same
manner as /VGA or the hateful /CRASHDEBUG :-)

Mail any comments, success/failure reports to:
ekarak@softlab.remove.ece.this.ntua.gr

void Legal_Mumbo_Jumbo()
{/*
 NOTE: 	The information contained herein is _not_ official whatsoever.
	I won't be held responsible for any damage of equipment.
	Examine your UPS manual for the usage of the UPS's communications port,
	it might vary from model to model, or from build to build.
	Use this at your own risk.
	(You can't say I didn't warn you!)
 */
};

-------------------------------------------------------------------------------------
Computer's serial port			|		UPS communications port
RS-232	|Pins				|		Pins
Signals	|DB9(DB25)			|		DB9	Meaning
--------|-------------------------------|-------------------------------------------
CD	|1(8)	o-------------\		|
        |          +--/\/\/\--+-------..|.. --------o	7	Low Battery Warning
	|	   | 4,7 kOhm		|			(Negative)*
RTS	|7(4)	o--+			|
	|	   | 4,7 kOhm		|
	|	   +-/\/\/\---+-------..|.. --------o	9	Power Failure Warning
CTS	|8(5)	o-------------/		|			(Negative)*
	|				|
DTR	|4(20)	o---------------------..|.. --------o	3	Remote UPS Shutdown
	|				|			(Positive)*
	|				|
0 V	|5(7)	o---------------------..|.. --------o	5	Signal Common
-------------------------------------------------------------------------------------

* these polarities are to be used in the UPS applet of the NT Control Panel