HT45F4M View Datasheet(PDF) - Holtek Semiconductor

Part Name

Description

Manufacturer

HT45F4M

Lithium Battery Backup Power ASSP MCU

Holtek Semiconductor 

HT45F4M

Lithium Battery Backup Power ASSP MCU

For instructions involving branches, such as jump or call instructions, two machine 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.

1

M O V A ,[1 2 H ]

2

C A LL D E LA Y

3

C P L [1 2 H ]

4

:

5

:

6 D E LA Y : N O P

F e tc h In s t. 1

E x e c u te In s t. 1

F e tc h In s t. 2

E x e c u te In s t. 2

F e tc h In s t. 3

F lu s h P ip e lin e

F e tc h In s t. 6

E x e c u te In s t. 6

F e tc h In s t. 7

Instruction Fetching

Program Counter

During program execution, the Program Counter is used to keep track of the address of the

next instruction to be executed. It is automatically incremented by one each time an instruction

is executed except for instructions, such as “JMP” or “CALL” that demand a jump to a non-

consecutive Program Memory address. Only the lower 8 bits, known as the Program Counter Low

Register, are directly addressable by the application program.

When executing instructions requiring jumps to non-consecutive addresses such as a jump instruction,

a subroutine call, interrupt or reset, etc., the microcontroller manages program control by loading the

required address into the Program Counter. For conditional skip instructions, once the condition has

been met, the next instruction, which has already been fetched during the present instruction execution,

is discarded and a dummy cycle takes its place while the correct instruction is obtained.

Program Counter

Program Counter High byte

PCL Register

PC10~PC8

PCL7~PCL0

The lower byte of the Program Counter, known as the Program Counter Low register or PCL, is

available for program control and is a readable and writeable register. By transferring data directly

into this register, a short program jump can be executed directly, however, as only this low byte

is available for manipulation, the jumps are limited to the present page of memory, that is 256

locations. When such program jumps are executed it should also be noted that a dummy cycle

will be inserted. Manipulating the PCL register may cause program branching, so an extra cycle is

needed to pre-fetch.

Rev. 1.10

15

January 15, 2013

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