This article was previously published under Q102711
The APC Smart-UPS series models 900, 900XL, 1250, and 2000 systemsinclude a standard RS-232 line failure output and UPS shutdown input.The low battery signal, however, is not a standard RS-232 signal andrequires special configuration for use with Windows NT.
For RS-232 outputs and inputs, the line failure, low battery, and UPSshutdown signals can be connected from the UPS to one of the computersRS-232 (serial) ports. Because the low battery signal generated by theAPC Smart-UPS is an open collector output, it must be pulled up to acommon reference voltage by means of a pullup resistor.
Following is the configuration for a cable that can be used with theAPC Smart-UPS series, including the implementation of the pullupresistor.
The above diagram indicates that Pin #5 on the PC serial port shouldbe connected directly to pin 4 on the UPS side, pin 8 to pin 2, pin 4to pin 1, and pin 1 to pin 5. In addition, pins 5 and 8 on the sameside (the UPS side) have a 10k ohm (10,000 ohm) resistor connectedbetween them. This resistor serves to pull the voltage on thisnon-RS-232 output high until an actual low voltage is generated by alow battery condition.
With the above cable, the following polarities should be set in theUPS section of the Control Panel: