D17133CS datasheet(80/289 Pages) NEC

80 / 289 page

CHAPTER 7

SYSTEM REGISTER (SYSREG)

7.8 CAUTIONS ON USE OF THE SYSTEM REGISTER

7.8.1 Reserved Words for Use with the System Register

Because the system register is allocated in data memory, it can be used in any of the data memory manipulation

instructions. As shown in Example 1 (using a 17K Series Assembler - AS17K), because a data memory address can

not be directly specified in an instruction operand, it needs to be defined as a symbol beforehand.

The system register is data memory, but has specialized functions which make it different from general-purpose

data memory. Because of this, the system register is used by defining it beforehand with symbols (used as reserved

words) in the assembler (AS17K).

Reserved words for use with the system register are allocated in address locations 74H to 7FH. They are defined

by the symbols (AR3, AR2, ..., PSW) shown in Figure 7-2.

As shown in Example 2, if these reserved words are used, it is not necessary to define symbols.

For information concerning reserved words, refer to CHAPTER 19 ASSEMBLER RESERVED WORDS.

Example 1.

MOV

34H, #0101B

;

Using a data memory address like 34H or 76H will

MOV

76H, #1010B

;

cause an error in the assembler.

M037

MEM

0.37H

;

Addresses in general data memory need to be

MOV

M037, #0101B

;

defined as symbols using the MEM pseudo instruction.

MOV

AR1, #1010B

;

By using the reserved word AR1 (address 76H),

;

there is no need to define the address as a symbol.

;

Reserved word AR1 is defined in a device file with

;

the pseudo instruction "AR1 MEM 0.76H".

Assembler AS17K has the below flag symbol handling instructions defined as macros.

SETn:

Set a flag to 1

CLRn:

Rest a flag to 0

SKTn:

Skip when all flags are 1

SKFn:

Skip when all flags are 0

NOTn:

Invert a flag

INITFLG:

Initialize a flag

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