Question: What could cause an instruction to be skipped?

[fschutt]

I'm sorry if this isn't the right place to ask, but it's hard getting someone with assembly experience.

I'm going through the tutorials (thanks a lot!) and I have this code:

org 100h
mov ax, 0800h
mov ds, ax
mov si, c[3]
ret

c DW 5 DUP(09h)

When I'm stepping through the code, the instruction mov si, c[3] doesn't do anything (I'd expect it to set SI to 0009). If I write it like this, however:

org 100h
mov si, c[3]
ret

c DW 5 DUP(09h)

... then it works. Is this intended somehow or is this a bug in the emulator? Does SI depend on other things to be set to certain values? If I use ax instead of si, it only changes ah for some reason. Could you replicate this or is this intentional? Thanks in advance.

[gurugio]

mov ax, 0800h
mov ds, ax
Those commands set ds=0800h.
So, "mov si, c[3]" command is "mov si, ds:c[3]", and it means "mov si, 0800:c[3]".
What is the address of c array?
Is the segment address of c array 0800h?

The second source does not change the segment address.
So it can read the c array.

[fschutt]

Thanks a lot for the answer!