编写两个十六位数的加法程序。

有两个十六位无符号数，分别存放在从20H和30H开始的数据区中，低八位先存，高八位在后，和存于R3（高八位）和R4（低八位），进位位存于R2。-Write two sixteen digits addition program.

There are two 16 bit unsigned number, respectively in from 20 h and 30 h began to data area, low eight put first, high eight of the, and stored in R3 (high eight) and R4 (low 8), carry a stored in R2.