ST10F280 datasheet(38/186 Pages) STMICROELECTRONICS

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ST10F280

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6 - CENTRAL PROCESSING UNIT (CPU)

The CPU includes a 4-stage instruction pipeline, a

16-bit arithmetic and logic unit (ALU) and dedi-

cated SFRs. Additional hardware has been added

for a separate multiply and divide unit, a bit-mask

generator and a barrel shifter.

Most of the ST10F280’s instructions can be exe-

cuted in one instruction cycle which requires 50ns

at 40MHz CPU clock. For example, shift and

rotate instructions are processed in one instruc-

tion cycle independent of the number of bits to be

shifted.

Multiple-cycle instructions have been optimized:

branches are carried out in 2 cycles, 16 x 16 bit

multiplication in 5 cycles and a 32/16 bit division in

10 cycles.

The jump cache reduces the execution time of

repeatedly performed jumps in a loop, from

2 cycles to 1 cycle.

The CPU uses a bank of 16 word registers to run

the current context. This bank of General Purpose

Registers (GPR) is physically stored within the

on-chip Internal RAM (IRAM) area. A Context

Pointer

(CP)

determines

the

base

address of the active register bank to be accessed

by the CPU.

The number of register banks is only restricted by

the available Internal RAM space. For easy

parameter passing, a register bank may overlap

others.

A system stack of up to 1024 bytes is provided as

a storage for temporary data. The system stack is

allocated in the on-chip RAM area, and it is

accessed by the CPU via the stack pointer (SP)

Two separate SFRs, STKOV and STKUN, are

implicitly compared against the stack pointer

value upon each stack access for the detection of

a stack overflow or underflow.

Figure 9 : CPU Block Diagram (MAC Unit not included)

Internal

RAM

2K Byte

General

Purpose

Registers

R15

MDH

MDL

Barrel-Shift

Mul./Div.-HW

Bit-Mask Gen.

ALU

16-Bit

STKOV

STKUN

Exec. Unit

Instr. Ptr

4-Stage

Pipeline

PSW

SYSCON

BUSCON 0

BUSCON 1

BUSCON 2

BUSCON 3

BUSCON 4

ADDRSEL 1

ADDRSEL 2

ADDRSEL 3

ADDRSEL 4

Data Pg. Ptrs

Code Seg. Ptr.

CPU

512K Byte

Flash

memory

Bank

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