UPD17P136ACT datasheet(72/292 Pages) NEC

72 / 292 page

CHAPTER 7 SYSTEM REGISTER (SYSREG)

7.5.5 IXE = 1 and MPE = 0 (Index Modification)

As shown in Figure 7-9, 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).

An example is shown below.

Example 1. Execution of “ADD r, m” 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

PSW, #.DF.IXE AND 0FH ; IXE

← 1

ADD

R003, M061

; (0.03H)

← (0.03H) + (0.73H)

As shown in Figure 7-12, 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 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 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.

UPD17P136ACT Datasheet(PDF) 72 Page - NEC

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