Thanks Jan,

But why the address for I1_8 is 01000H rather than something else? Can you explain why we can read from:

01000H for input from 1 - 8
00800H for input from 9 - 16
00400H for input from 17 - 24

and

08000H for output from 1 - 8
04000H for output from 9 - 16
02000H for output from 17 - 24

One of the difference in between 2 micro controller is:

1. AT89S8252 has 8K memory:

"The Code and Data memory arrays are mapped via separate address spaces in the
serial programming mode. In the parallel programming mode, the two arrays occupy
one contiguous address space: 0000H to 1FFFH for the Code array and 2000H to
27FFH for the Data array"

(AT89S8252 datasheet, page 23)

2. AT89S8253 has 12K Flash memory:
"The code and data memory arrays are mapped via separate address spaces in the parallel and
serial programming modes: 0000H to 2FFFH for code memory and 3000H to 37FFH for data
memory"

(AT89S8253 datasheet - Page 36, the address 3000H - 37FFH are corrected by Atmel technical support recently)

Would this change affect the read and write addresses mentioned above? And if yes, then what are new addresses given for each input and output banks?