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ST20-C1

Instruction Set Reference Manual

STMicroelectronics 

2.1 Instruction listings

2 Notation

This chapter describes the notation used throughout this manual, including the

meaning of the instruction listings and the meanings and values of constants.

2.1 Instruction listings

The instructions are listed in alphabetical order, one to a page. Descriptions are

presented in a standard format with the instruction mnemonic and full name of the

instruction at the top of the page, followed by these categories of information:

• Code: the instruction code;

• Description: a brief summary of the purpose and behavior of the instruction;

• Definition: a more formal and complete description of the instruction, using

the notation described below in section 2.2;

• Status Register: a list of errors and other changes to the Status Register

which can occur;

• Comments: a list of other important features of the instruction;

• See also: cross references are provided to other instructions with related func-

tions.

These categories are explained in more detail below, using the and instruction as an

example.

2.1.1 Instruction name

The header at the top of each page shows the instruction mnemonic and, on the right,

the full name of the instruction. For primary instructions the mnemonic is followed by

‘n’ to indicate the operand to the instruction; the same notation is used in the descrip-

tion to show how the operand is used. An explanation of the primary and secondary

instruction formats is given in section 3.4.

2.1.2 Code

The code of the instruction is the value that would appear in memory to represent the

instruction.

For secondar y instructions the instruction ‘operation code’ is shown as the memory

code — the actual bytes, including any prefixes, which are stored in memory. The

value is given as a sequence of bytes in hexadecimal, decoded left to right. The codes

are stored in memory in ‘little-endian’ format, with the first b yte at the lowest address.

For example, the entry for the and instruction is:

Code: F9

This means that the hexadecimal byte value F9 would appear in memory for an and.

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