HT36A2 datasheet(6/24 Pages) HOLTEK

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HT36A2

Rev. 1.00

June 19, 2003

Function Description

Execution Flow

The system clock for the HT36A2 is derived from either

a crystal or an RC oscillator. The oscillator frequency di-

vided by 2 is the system clock for the MCU and it is inter-

nally 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 one instruction cycle while de-

coding and execution takes the next instruction cycle.

However, the pipelining scheme causes each instruc-

tion to effectively execute in one cycle. If an instruction

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 and its contents specify a maximum of 8192 ad-

dresses for each bank.

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

subroutine, the PC manipulates the program transfer by

loading the address corresponding to each instruction.

The conditional skip is activated by instruction. Once the

condition is met, the next instruction, fetched during the

current instruction execution, is discarded and a dummy

cycle replaces it to retrieve the proper instruction. Other-

wise 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 256 locations.

Once a control transfer takes place, an additional

dummy cycle is required.

Program ROM

HT36A2 provides 16 address lines WA[15:0] to read the

Program ROM which is up to 1M bits, and is commonly

used for the wavetable voice codes and the program

memory. It provides two address types, one type is for

program ROM, which is addressed by a bank pointer

PF2~0 and a 13-bit program counter PC 12~0; and the

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 f M C U

( S y s t e m C l o c k / 2 )

P C

Execution flow

Mode

Program Counter

*12

*11

*10

Initial Reset

0000000000

Timer/Event Counter 0 Overflow

0000001000

Timer/Event Counter 1 Overflow

0000001100

Skip

PC+2

Loading PCL

*12

*11

*10

Jump, Call Branch

#12

#11

#10

Return From Subroutine

S12

S11

S10

Program counter

Note:

*12~*0: Bits of Program Counter

@7~@0: Bits of PCL

#12~#0: Bits of Instruction Code

S12~S0: Bits of Stack Register

@7~@0: Bits of PCL

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