A top down/bottom up covering for an architectural opening comprising in combination: a headrail; at least two horizontally disposed vertically movable rails (48, 50) supporting at least one panel of collapsible shade material; and at least two flexible lift cords affixed to each rail (48, 50); characterised by: a control system component (54A, 54B) associated with each rail (48, 50), each component (54A, 54B) including an elongated drive shaft, a system for reciprocally and reversibly rotating said drive shaft about its longitudinal axis, a wrap spool (86C, 86E) rotatable with said drive shaft and connected to a lift cord (90C, 90E) such that said lift cord (90C, 90E) can be wrapped about or unwrapped from said wrap spool (86C, 86E), vertical movement of said rails (48, 50) being effected by wrapping and unwrapping of said lift cords (90C, 90E) about said spools (86C, 86E), and a cord tension control system for preventing said lift cords (90C, 90E) from becoming entangled at said wrap spools (86C, 86E), said cord tension control system including a threaded shaft associated with and rotatable in unison with each drive shaft, a nut threaded on each of said threaded shafts for translating movement along an associated shaft, the nuts on said threaded shafts overlapping in their path of travel along an associated threaded shaft whereby upon engagement of said nuts with an adjacent nut the drive shafts will be prohibited from rotating in a predetermined direction thereby prohibiting the wrap spools (86C, 86E) on said drive shafts from rotating. a headrail; at least two horizontally disposed vertically movable rails (48, 50) supporting at least one panel of collapsible shade material; and at least two flexible lift cords affixed to each rail (48, 50); characterised by: a control system component (54A, 54B) associated with each rail (48, 50), each component (54A, 54B) including an elongated drive shaft, a system for reciprocally and reversibly rotating said drive shaft about its longitudinal axis, a wrap spool (86C, 86E) rotatable with said drive shaft and connected to a lift cord (90C, 90E) such that said lift cord (90C, 90E) can be wrapped about or unwrapped from said wrap spool (86C, 86E), vertical movement of said rails (48, 50) being effected by wrapping and unwrapping of said lift cords (90C, 90E) about said spools (86C, 86E), and a cord tension control system for preventing said lift cords (90C, 90E) from becoming entangled at said wrap spools (86C, 86E), said cord tension control system including a threaded shaft associated with and rotatable in unison with each drive shaft, a nut threaded on each of said threaded shafts for translating movement along an associated shaft, the nuts on said threaded shafts overlapping in their path of travel along an associated threaded shaft whereby upon engagement of said nuts with an adjacent nut the drive shafts will be prohibited from rotating in a predetermined direction thereby prohibiting the wrap spools (86C, 86E) on said drive shafts from rotating. a control system component (54A, 54B) associated with each rail (48, 50), each component (54A, 54B) including an elongated drive shaft, a system for reciprocally and reversibly rotating said drive shaft about its longitudinal axis, a wrap spool (86C, 86E) rotatable with said drive shaft and connected to a lift cord (90C, 90E) such that said lift cord (90C, 90E) can be wrapped about or unwrapped from said wrap spool (86C, 86E), vertical movement of said rails (48, 50) being effected by wrapping and unwrapping of said lift cords (90C, 90E) about said spools (86C, 86E), and a cord tension control system for preventing said lift cords (90C, 90E) from becoming entangled at said wrap spools (86C, 86E), said cord tension control system including a threaded shaft associated with and rotatable in unison with each drive shaft, a nut threaded on each of said threaded shafts for translating movement along an associated shaft, the nuts on said threaded shafts overlapping in their path of travel along an associated threaded shaft whereby upon engagement of said nuts with an adjacent nut the drive shafts will be prohibited from rotating in a predetermined direction thereby prohibiting the wrap spools (86C, 86E) on said drive shafts from rotating.