Z8 Encore! XP® 4K Series
Product Specification
191
eZ8 CPU Instruction Set
Assembly Language Programming Introduction
The eZ8 CPU assembly language provides a means for writing an application program
without concern for 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 state-
ments. Each statement can contain labels, operations, operands and comments.
Labels can be assigned to a particular instruction step in a source program. The label iden-
tifies 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 lan-
guage program called the object code. The object code is executed by the eZ8 CPU. An
example segment of an assembly language program is detailed in the following example.
Assembly Language Source Program Example
JP START
START:
; Everything after the semicolon is a comment.
; A label called “START”. The first instruction (JP START) in this
; example causes program execution to jump to the point within the
; program where the STARTlabel occurs.
LD R4, R7
; A Load (LD) instruction with two operands. The first operand,
; Working Register R4, is the destination. The second operand,
; Working Register R7, is the source. The contents of R7 is
; written into R4.
LD 234H, #%01 ; Another Load (LD) instruction with two operands.
; The first operand, Extended Mode Register Address 234H,
; identifies the destination. The second operand, Immediate Data
; value 01H, is the source. The value 01His written into the
; Register at address 234H.
PS022815-0206
eZ8 CPU Instruction Set
ZILOG [ ZILOG, INC. ]
