Accu 1 and accu 2 are added and the result is stored in accu 1. As long as the values in accu 1 and accu 2 are positive it is indifferent whether they are loaded out of a word or a dword. But if one of the as word loaded operands can be negative ‘+D’ will lead to absurd results. In this case the eventually negative operand has to be extended to the dword format with the operation ITD before adding.
L L#300000
L MD 8
+D
T MD 20
See also:
EN-input and ENO-output