HT82M99EE_08 datasheet(6/44 Pages) HOLTEK

6 / 44 page

HT82M99EE/HT82M99AE

Rev. 1.50

December 22, 2008

Functional Description

Execution Flow

The system clock for the microcontroller is derived from

either 6MHz or 12MHz crystal oscillator, which used a

frequency that is determined by the SCLKSEL bit of the

SCC Register. The default system frequency is 12MHz.

The system clock is internally divided 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 an instruction cycle while de-

coding and execution takes the next instruction cycle.

However, the pipelining scheme causes each instruc-

tion to be effectively executed in a cycle. If an instruction

changes the program counter, two cycles are required to

complete the instruction.

Program Counter

- PC

The program counter (PC) controls the sequence in

which the instructions stored in the program ROM are

executed and its contents specify a full range of pro-

gram memory.

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 to the PCL register, performing a sub-

routine call or return from subroutine, initial reset,

internal interrupt, external interrupt or return from inter-

rupts, the PC manipulates the program transfer by load-

ing the address corresponding to each instruction.

The conditional skip is activated by instructions. Once

the condition is met, the next instruction, fetched during

the current instruction execution, is discarded and a

dummy cycle replaces it to get the proper instruction.

Otherwise proceed with the next instruction.

The lower byte of the program counter (PCL) is a read-

able and writeable register (06H). Moving data into the

PCL performs a short jump. The destination will be

within the current program ROM page.

When a control transfer takes place, an additional

dummy cycle is required.

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 2 ( R C o n l y )

P C

Execution Flow

Mode

Program Counter

*10

Initial Reset

00000000000

USB Interrupt

00000000100

Timer/Event Counter Overflow

00000001100

Skip

Program Counter+2

Loading PCL

*10

Jump, Call Branch

#10

Return from Subroutine

S10

Program Counter

Note: *10~*0: Program counter bits

S10~S0: Stack register bits

#10~#0: Instruction code bits

@7~@0: PCL bits

HT82M99EE Datasheet(PDF) 6 Page - Holtek Semiconductor Inc

HT82M99EE Datasheet(HTML) 6 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Download

Link URL