Zilog EZ80F916 - Manual (Page 61)

eZ80
®
CPU
User Manual
UM007715-0415 CPU Instruction Set
52
CPU Instruction Set
eZ80
®
CPU Assembly Language Programming Introduction
eZ80 ® CPU assembly language provides a means for writing an application program
without considering the actual memory addresses or machine instruction formats. A
program written in assembly language is called a source program. Assembly language
allows the use of symbolic addresses to identify memory locations. It also allows
mnemonic codes (opcodes and operands) to represent the instructions themselves. The
opcodes identify the instruction while the operands represent memory locations, registers,
or immediate data values.
Each assembly language program consists of a series of symbolic commands called
statements. Each statement contains labels, operations, operands, and comments.
Labels are assigned to a particular instruction step in a source program. The label
identifies that step in the program as an entry point for use by other instructions.
The assembly language also includes assembler directives that supplement the machine
instruction. The assembler directives, or pseudo-ops, are not translated into a machine
instruction. Rather, the pseudo-ops are interpreted as directives that control or assist the
assembly process.
The source program is processed (assembled) by the assembler to obtain a machine
language program called the object code. The object code is executed by the CPU.
An example segment of an assembly language source program is detailed in the following
example.
Assembly Language Source Program Example
JP.LIL START ;Everything after the semicolon is

;a comment.
.ASSUME ADL = 1 ;A compiler directive or pseudo-op.
START: ;A label called “START”. The first
;instruction in this example causes program
;execution to jump to the point within the
;program where the JP.LIL (Jump) executes.
LD A, 3Ah ;A Load (LD) instruction with two operands.
;The accumulator register, A, is the first
;operand that indicates the destination for
;this instruction. The hexadecimal constant
;value 3Ah is the second operand signifying
;the source value for this instruction.
eZ80
®
CPU assembly language is designed to minimize the number of different opcodes
corresponding to the set of basic machine operations, in addition to providing a consistent