Direct Addressing
6-4
6.3
Direct Addressing
In direct addressing, the data address is formed by the concatenation of the
eight LSBs of the data-page pointer (DP) with the 16 LSBs of the instruction
word (expr). This results in 256 pages (64K words per page), allowing you to
access a large address space without requiring a change of the page pointer.
The syntax and operation for direct addressing are:
Syntax:
@expr
Operation:
address = DP concatenated with expr
Figure 6–1 shows the formation of the data address. Example 6–1 is an instruc-
tion example with data before and after instruction execution.
Figure 6–1. Direct Addressing
0
0
31
16
15
0
0
0
31
address
operand
page
expr
x
x . . . x
x
0 . . . 0
31
8
7
0
24
23
31
DP
Instruction
word
(Data-
page pointer)
Example 6–1. Direct Addressing
ADDI
@0BCDEh,R7
Before Instruction
After Instruction
R7
00 0000 0000
R7
00 1234 5678
DP
8A
DP
8A
Data memory
8ABCDEh
1234 5678
8ABCDEh
1234 5678