Zilog Z16F2810 - Manual (Page 19)

UM018809-0611 Architectural Overview
ZNEO
®
CPU Core
User Manual
3
Fetch Unit
The Fetch Unit’s primary function is to fetch opcodes and operand words (including
immediate data) from memory. The Fetch Unit also fetches interrupt vectors. The Fetch
Unit is pipelined and operates semi-independently from the execution unit. This Unit per-
forms a partial decoding of the opcode to determine the number of bytes to fetch for the
operation.
The Fetch Unit operation sequence functions as follows:
1. Fetch the first 2-byte opcode word.
2. Determine number of remaining opcode and operand words (one or two).
3. Fetch the remaining opcode and operand words.
4. Present the opcode and operands to the Instruction State Machine.

A ZNEO CPU instruction is always 1, 2, or 3 words long, including operands, and must be
aligned on an even address.
Figure 1. ZNEO CPU Block Diagram
Fetch Unit
Instruction and
Operand Fetch
Instruction State Machine
Arithmetic Logic Unit (ALU)
32-bit ALU Registers, R0-R15
Bus Arbiter
16
Internal
Non-volatile
Memory
16
Internal
RAM
8/16
Internal I/O
8/16
External
Memory
Interface
Program
Counter
Control
Registers
Execution Unit