Accu 1 is substracted of accu 2 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 an absurd result. In this case the eventually negative operand has to be extended to the dword format with the operation ITD before substracting.
L L#300000
L MD 8
-D
T MD 20 // in MD 20 is now displayed 300000 - MD8
See also:
EN-input and ENO-output