Zilog Z16F2810 - Manual (Page 20)

Architectural Overview UM018809-0611
4
ZNEO
®
CPU Core
User Manual
Execution Unit
The Execution Unit performs the processing functions required by the instruction opcodes
and operands which it receives from the Fetch Unit.
Instruction State Machine
The Instruction State Machine is the controller for the ZNEO CPU Execution Unit. After
the initial operation decode by the Fetch Unit, the Instruction State Machine takes over
and completes the instruction. The Instruction State Machine generates effective addresses
and controls memory read and write operations.
Program Counter
The Program Counter contains a counter and adder to monitor the address of the current
instruction and calculates the next instruction address. According to the number of bytes
fetched by the Fetch Unit, the Program Counter increments automatically. The adder
increments and handles Program Counter jumps for relative addressing. The initial value
of the program counter is programmable through the RESET vector.
refer to the ZNEO product specification that is specific to your device for the RESET vec-
tor location.
Programs cannot address the Program Counter directly but the instruction
LEA Rd, 4(PC) can be used to load the current Program Counter value (the next instruc-
tion address) into an ALU Register. The JP, CALL, and related instructions are used to
alter the program counter value.
The I/O memory register described in Program Counter Overflow Register on page 9 pro-
vides access to the program counter overflow feature.
Arithmetic Logic Unit
The Arithmetic Logic Unit (ALU) performs arithmetic and logical operations on data.
arithmetic operations including addition, subtraction, and multiplication. Logical opera-
tions include binary logic operations, bit shifting, and bit rotation.
ALU Registers
The ZNEO CPU provides 16 highly efficient 32-bit registers associated with the ALU.
The 16 ALU registers are named from R0 to R15.
These registers have the following characteristics:
•
The CPU can access ALU registers more quickly than ordinary internal or external
memory.
Note: