Library /sys$common/syshlp/ncphelp.hlb SET, CIRCUIT, ACTIVE BASE base  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Applies to DDCMP CONTROL circuits.  This value indicates the base
 priority of an ACTIVE tributary after the tributary has been
 polled.  You can indicate a separate base for each of the
 indicated polling states.  The base value must be a decimal
 integer from 0 to 255.  The ACTIVE BASE default is 255.