if bits 10&11 = 00 (it mean i don't care them in my program), when you command stop drive, Decel Time 2 (Par. 538) not used.
if bits 11 = 1 bit 10=0 when you command stop drive, Decel Time 2 (Par. 538) used.
http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/750-pm001_-en-p.pdf page 241.