Two registers can be cleared simultaneously by executing an LSUB instruction:
LSUB d, e, d, d, c
will clear d and e in a single clock cycle, provided the bottom bit of c is zero. It will provide all ones in both d and e if c is one. If any register c is known to contain a word address, the instruction:
LSUB d, e, c, c, c
will clear both s and e. Similarly, LADD can be used to copy oen register and clear another register simultaneously.