Addressing Modes Help

[halt4814]

I need assistance with addressing modes. I have a chart...

LDA 200 | Address field=200
ADD IMMEDIATE 301 | ?
LDA INDIRECT 100 | ?
ADD BASE REGISTER 100 | ?
LDA INDEXING 100 | Address field=100+100=200

I cannot figure out the three middle answers at all. Can I get any help on this?

[halt4814]

I forgot the table with it as well

PC 90
BR 100
XR 100
AC 0

[Eri523]

LDA INDIRECT 100 | ?

That doesn't seem to quite make sense to me. The nature of indirect addressing usually is to take the address to refer to from a register instead of a field in the instruction. So what's the 100 for? Except perhaps this is meant to take the address of the memory location to be eventually addressed from memory location 100. AFAICT that would then be referred to as multi-level memory indirect addressing which is rather unusual. And then you'd still need to know the content of memory location 100...

ADD BASE REGISTER 100 | ?
LDA INDEXING 100 | Address field=100+100=200

I can't really tell from the context what should be the difference between the two, unless perhaps one of them is meant to be scaled-indexed addressing, but then you'd need to know the scale factor.

In the meantime perhaps this can give you some clues: http://en.wikipedia.org/wiki/Addressing_mode

Ah, and... None of them is a three-operand instruction form, of course.