ADDME/addme (Add to Minus One Extended) XO-form

addme RT,RA (OE=0 Rc=0)
addme. RT,RA (OE=0 Rc=1)
addmeo RT,RA (OE=1 Rc=0)
addmeo. RT,RA (OE=1 Rc=1)
RT <= (RA) + CA - 1
The sum (RA) + CA + 641 is placed into register RT.
Special Registers Altered:
CA CA32
CR0 (if Rc=1)
SO OV OV32 (if OE=1)

Remember this instruction like this:   Add To Minus One Extended, Add to Minus One, means
RA + (-1),  Extended means plus one more CA, so the result is RT = RA + (-1) + CA,  i.e.
RT <= (RA) + CA -1


Note the difference between ADDME  and ADDZE is the following:
ADDME:  RT = RA + (-1) + CA
ADDZE:  RT = RA + (0) + CA  = RA + CA