HT45F23 datasheet(20/152 Pages) HOLTEK

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System Architecture

A key factor in the high-performance features of the Holtek range of microcontrollers is attributed to

the internal system architecture. The range of devices take advantage of the usual features found

within RISC microcontrollers providing increased speed of operation and enhanced performance. The

pipelining scheme is implemented in such a way that instruction fetching and instruction execution are

overlapped, hence instructions are effectively executed in one cycle, with the exception of branch or

call instructions. An 8-bit wide ALU is used in practically all operations of the instruction set. It carries

out arithmetic operations, logic operations, rotation, increment, decrement, branch decisions, etc. The

internal data path is simplified by moving data through the Accumulator and the ALU. Certain internal

registers are implemented in the Data Memory and can be directly or indirectly addressed. The simple

addressing methods of these registers along with additional architectural features ensure that a

minimum of external components is required to provide a functional I/O and A/D control system with

maximum reliability and flexibility. This makes the device suitable for low-cost, high-volume

production for controller applications.

Clocking and Pipelining

The main system clock, derived from either a Crystal/ Resonator or RC oscillator is subdivided into

four internally generated non-overlapping clocks, T1~T4. The Program Counter is incremented at the

beginning of the T1 clock during which time a new instruction is fetched. The remaining T2~T4

clocks carry out the decoding and execution functions. In this way, one T1~T4 clock cycle forms one

instruction cycle. Although the fetching and execution of instructions takes place in consecutive

instruction cycles, the pipelining structure of the microcontroller ensures that instructions are

effectively executed in one instruction cycle. The exception to this are instructions where the contents

of the Program Counter are changed, such as subroutine calls or jumps, in which case the instruction

will take one more instruction cycle to execute.

For instructions involving branches, such as jump or call instructions, two instruction cycles are

required to complete instruction execution. An extra cycle is required as the program takes one cycle to

first obtain the actual jump or call address and then another cycle to actually execute the branch. The

requirement for this extra cycle should be taken into account by programmers in timing sensitive

applications.

Rev. 1.20

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

F e t c h I n s t . ( P C )

E x e c u t e I n s t . ( P C - 1 )

F e t c h I n s t . ( P C + 1 )

E x e c u t e I n s t . ( P C )

F e t c h I n s t . ( P C + 2 )

E x e c u t e I n s t . ( P C + 1 )

P C

P C + 1

P C + 2

O s c i l l a t o r C l o c k

( S y s t e m C l o c k )

P h a s e C l o c k T 1

P r o g r a m C o u n t e r

P h a s e C l o c k T 2

P h a s e C l o c k T 3

P h a s e C l o c k T 4

P i p e l i n i n g

System Clocking and Pipelining

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