HT86R384 datasheet(8/41 Pages) HOLTEK

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HT86R384

Rev. 0.10

May 18, 2007

Preliminary

Functional Description

Execution Flow

The system clock for the HT86R384 series is derived

from either a crystal or an RC oscillator. It is internally di-

vided into four non-overlapping clocks. One instruction

cycle consists of four system clock cycles.

Instruction fetching and execution are pipelined in such

a way that a fetch takes one instruction cycle while de-

coding and execution takes the next instruction cycle.

However, the pipelining scheme causes each instruc-

tion to effectively execute within one cycle. If an instruc-

tion changes the Program Counter, two cycles are

required to complete the instruction.

Program Counter

- PC

The 13-bit Program Counter (PC) controls the sequence

in which the instructions stored in program ROM are ex-

ecuted.

After accessing a program memory word to fetch an in-

struction code, the contents of the Program Counter are

incremented by one. The Program Counter then points

to the memory word containing the next instruction

code.

When executing a jump instruction, conditional skip ex-

ecution, loading PCL register, subroutine call, initial re-

set, internal interrupt, external interrupt or return from

Mode

Program Counter

*12

*11

*10

Initial Reset

0000000000000

External or Serial Input Interrupt

0000000000100

Timer/Event Counter 0 Overflow

0000000001000

Timer/Event Counter 1 Overflow

0000000001100

Timer Counter 2 Overflow

0000000010000

Timer Counter 3 Overflow

0000000010100

Skip

Program Counter+2

Loading PCL

*12

*11

*10

Jump, Call Branch

#12

#11

#10

Return from Subroutine

S12

S11

S10

Program Counter

Note: *12~*0: Program Counter bits

S12~S0: Stack register bits

#12~#0: Instruction code bits

@7~@0: PCL bits

T 1

T 2

T 3

T 4

T 1

T 2

T 3

T 4

T 1

T 2

T 3

T 4

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

S y s t e m C l o c k

O S C ( R C o n l y )

P C

P 1

P 2

P 3

P 4

I n t e r n a l

P h a s e

C l o c k s

Execution Flow

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