NEC mPD17120 Subseries, User Manual

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CHAPTER 7 SYSTEM REGISTER (SYSREG)
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7.5.5 MPE=0 and IXE=1 (Index Modification)
As shown in Figure 7-8, when a data memory manipulation instruction is executed, any bank or address in data
memory specified by m can be modified using the index register.
When indirect data transfer using the general register (MOV @r, m or MOV m, @r) is executed, the indirect transfer
bank and address specified by @r can be modified using the index register.
Address modification is done by performing an OR operation on the data memory address and the index register.
The data memory manipulation instruction being executed manipulates data in the memory location pointed to by
the result of the operation (called the real address).
Examples are shown below.
Example 1. When the general register is in row address 0
R003 MEM 0.03H
M061 MEM 0.61H
MOV IXL, #0010B ; IX
←
00000010010B
MOV IXM, #0001B ;
MOV IXH, #0000B ; MPE
←
0
OR PSW, #.DF.IXE AND 0FH ; IXE
←
1
ADD R003, M061
As shown in Figure 7-11, when the instructions of Example 1 are executed, the value in data
memory address 73H (real address) and the value in general register address R003 (address
location 03H) are added together and the result is stored in general register address R003.
When the ADD r, m instruction is executed, the data memory address specified by m (address
61H in above example) is index modified.
Modification is done by performing an OR operation on data memory location M061 (address
61H, binary 00001100001B) and the index register (00000010010B in the above example).
The result of the operation (00001110011B) is used as a real address (address location 73H)
by the instruction being executed.
As compared to when IXE=0 (Examples in 7.5.3 ), in this example the data memory address
being directly specified by m is modified by performing an OR operation on m and the index
register.