Indirect Addressing in Computer Architechture

Defn

Indirect Addressing:

The address of the data is held in an intermediate location so that the address is first ‘looked up’ and then used to locate the data itself.

也就是說，要知道目標資料到底放在哪，要先去一個地址找到目標地址的實際地址在哪，有點像是郵政信箱。

Details

1) A specific block of memory will be used by the loader to store the starting address of every subroutine within the library. This block of memory is called a vector table. A vector table holds addresses rather than data. The application is informed by the loader of the location of the vector table itself.

2) In order for the CPU to get to the data, the code first of all fetches the content at RAM location 5002 which is part of the vector table.

3) The data it contains is then used as the address of the data to be fetched, in this case the data is at location 9000

A typical assembly language instruction would look like:

MOV A, @5002
# Look at location 5002 for the address which points to the target data.
# That address is then used to fetch data and load it into the accumulator.
# In this case: 302

Reference:

• teach-ict