D17133CS datasheet(75/289 Pages) NEC

75 / 289 page

CHAPTER 7

SYSTEM REGISTER (SYSREG)

7.6.2 Functions of the General Register Pointer

The general register pointer is used to specify the location of the general register in data memory. For a more

detailed explanation, refer to CHAPTER 8 GENERAL REGISTER (GR).

The general register consists of sixteen nibbles in any single row of data memory. As shown in Figure 7-15, the

general register pointer is used to indicate which row address is being used as the general register.

Since the general register pointer effectively consists of three bits, the data memory row addresses in which the

general register can be placed are address locations 0H to 7H of BANK0. In other words, any row in data memory

can be specified as the general register.

With the general register allocated in data memory, data can be transferred to and from, and arithmetic/logical

operations can be performed on the general register and data memory.

Note that addresses 40H to 6EH are uninstalled memory locations and should therefore not be specified as

locations for the general register.

For example, when instructions such as

ADD r,m and LD r,m

are executed, instruction operand r can specify an address in the general register and m specifies an address in data

memory. In this way, operations like addition and data transfer can be performed on and between data memory

and the general register.

Figure 7-15. General Register Configuration

Notes

1. These bits should not be specified in the case of the

µPD17120 and 17121.

2. This bit is allocated to BCD flag.

Note

RPH

RPL











Note 1

0123456789

A B C D E

General register (16 nibbles)

System register

BANK0

General register pointer

(RP)

Example :

General

with

RPH=0000B

RPL=010

×B

Area in which

general register

can be specified

Column address

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