SlavedScan
From The RadioReference Wiki
Slaved Scan
[Image:http://sites.google.com/site/radioetcetera/SlavedScan.jpg?attredirects=0]
This program connects to two Uniden DMA computer-controlled scanners via two separate serial ports. The program continuously queries each scanner to determine if it is stopped on a frequency. If it detects that both scanners are stopped on the same frequency at the same time, it will command the "slave" scanner to continue scanning so that both scanners are never monitoring the same frequency. The program will work with the following scanners:
BCD396T BCD396XT BCD996T BCT15 BC346XT BR330T
The program's website with download and user instructions can be found here