VR4102 datasheet(648/701 Pages) NEC

648 / 701 page

CHAPTER 27 CPU INSTRUCTION SET DETAILS

648

SWL

Store Word Left

SWL

base

SWL

1 0 1 0 1 0

offset

26 25

21 20

16 15

Format:

SWL rt, offset (base)

Description:

This instruction can be used with the SWR instruction to store the contents of a register into four consecutive

bytes of memory, when the bytes cross a word boundary. SWL stores the left portion of the register into the

appropriate part of the high-order word of memory; SWR stores the right portion of the register into the

appropriate part of the low-order word.

The SWL instruction adds its sign-extended 16-bit offset to the contents of general register base to form a virtual

address which may specify an arbitrary byte. It alters only the word in memory which contains that byte. From

one to four bytes will be stored, depending on the starting byte specified.

Conceptually, it starts at the most-significant byte of the register and copies it to the specified byte in memory;

then it copies bytes from register to memory until it reaches the low-order byte of the word in memory.

No address error exceptions due to alignment are possible.

address 4

address 0

memory

before

after

$24

SWL $24, 4 ($0)

address 4

address 0

VR4102 Datasheet(PDF) 648 Page - NEC