UPD17P136ACT datasheet(82/292 Pages) NEC

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CHAPTER 7 SYSTEM REGISTER (SYSREG)

7.8 NOTES CONCERNING USE OF THE SYSTEM REGISTER

7.8.1 Reserved Words for 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 coded 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. Therefore, the system register is used by defining it beforehand with symbols (used as reserved words)

in the assembler (AS17K).

Reserved words for the system register are allocated in address 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, see CHAPTER 20 ASSEMBLER RESERVED WORDS.

Example 1.

MOV

34H, #0101B

; Using a data memory address like 34H or 76H will cause an

MOV

76H, #1010B

; error in the assembler.

M037

MEM 0.37H

; Addresses in general data memory need to be defined as

MOV

M037, #0101B ; symbols using the MEM directive.

MOV

AR1, #1010B

; By using the reserved word AR1 (address 6H), there is no need

; to define the address as a symbol.

; Reserved word AR1 is defined in a device file with the directive

; “AR1 MEM 0.76H”.

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

SETn

: Set a flag to 1

CLRn

: Reset 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

By using these embedded macro instructions, data memory can be handled as flags as shown below in Example

The functions of the program status word and the memory pointer enable flag are defined in bit units (flag units)

and each bit has a reserved word defined for it. These reserved words are MPE, BCD, CMP, CY, Z and IXE.

If these flag reserved words are used, the embedded macro instructions can be used as shown in Example

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