Assembly Language Absolute addresses and segment registers

Question

a review problem lists these registers in hex:

cs = ????  sp = 0300  ax = a66a  ip = 01cf
ds = 4100  bp = 0003  bx = 1234  
ss = 48ee  si = 0100  cx = 00ff
es = 4cee  di = 1000  dx = 0000

1. The absolute address of the next instruction to be executed is 40f0f.

    40f0f -01cf _____ 40d40 / 10 = 40d4 = cs 

2. Is the size of the data segment in bytes always equal to the stack segment minus the data segment * 10? 48ee - 4100 = 7ee0. Likewise, is the code segment in bytes always equal to the data segment minus the code segment * 10? 48ee - 40d4 = 81a0.

3. For mov cx,[bx + si] , the absolute address of the source operand is 42334.

    bx = 1234 si = 0100 _________ 1334 ds = 4100 * 10 = 41000 + 1334 = 42334 

4. For mov cx,[di - 4] , the absolute address of the source operand is 41ffc.

    di = 1000 - 4 _________ 0FFC ds = 4100 * 10 = 41000 + 0ffc = 41ffc 

5. For mov cx,[bp + si - 3] , the absolute address of the source operand is 48fe0.

    bp = 0003 si = 0100 - 3 _________ 0100 ss = 48ee * 10 = 48ee0 + 0100 = 48fe0 

Am I going about solving these the right way? How do I know when to use the stack segment for these calculations and when to use the data segment?

Answer 1

For address calculations involving bp or sp or stack operations like push or pop the segment register is implicitly ss , for other addresses ds . Exception: If you use a string instruction, the destination segment register is implicitly es .