HT48F10E datasheet(9/74 Pages) HOLTEK

9 / 74 page

HT48F06E/HT48F10E/HT48F30E

Rev. 1.60

July 29, 2009

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

²JMP² or ²CALL², that demand a jump to a

non-consecutive Program Memory address. Note that

the Program Counter width varies with the Program

Memory capacity depending upon which device is se-

lected. However, it must be noted that only the lower 8

bits, known as the Program Counter Low Register, are

directly addressable by user.

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 condi-

tional skip instructions, once the condition has been

met, the next instruction, which has already been

fetched during the present instruction execution, is dis-

carded and a dummy cycle takes its place while the cor-

rect instruction is obtained.

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 writable 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 in-

serted.

The lower byte of the Program Counter is fully accessi-

ble under program control. Manipulating the PCL might

cause program branching, so an extra cycle is needed

to pre-fetch. Further information on the PCL register can

be found in the Special Function Register section.

Stack

This is a special part of the memory which is used to

save the contents of the Program Counter only. The

stack can have either 2 or 4 levels depending upon

which device is selected and is neither part of the data

nor part of the program space, and can neither be read

from nor written to. The activated level is indexed by the

Stack Pointer, SP, which can also neither be read from

nor written to. At a subroutine call or interrupt acknowl-

edge signal, the contents of the Program Counter are

pushed onto the stack. At the end of a subroutine or an

interrupt routine, signaled by a return instruction, RET or

RETI, the Program Counter is restored to its previous

value from the stack. After a device reset, the Stack

Pointer will point to the top of the stack.

If the stack is full and an enabled interrupt takes place,

the interrupt request flag will be recorded but the ac-

knowledge signal will be inhibited. When the Stack

Pointer is decremented, by RET or RETI, the interrupt

will be serviced. This feature prevents stack overflow al-

lowing the programmer to use the structure more easily.

However, when the stack is full, a CALL subroutine in-

struction can still be executed which will result in a stack

overflow. Precautions should be taken to avoid such

cases which might cause unpredictable program

branching.

Mode

Program Counter Bits

b10

Initial Reset

00000000000

External Interrupt

00000000100

Timer/Event Counter

Overflow

00000001000

Skip

Program Counter + 2

Loading PCL

PC10

PC9

PC8

Jump, Call Branch

#10

Return from Subroutine

S10

Program Counter

Note:

PC10~PC8: Current Program Counter bits

@7~@0: PCL bits

#10~#0: Instruction code address bits

S10~S0: Stack register bits

For the HT48F10E and the HT48F06E, since their Program Counter is 10 bits wide, the b10 column in the table

is not applicable.

HT48F10E 数据表(PDF) 9 Page - Holtek Semiconductor Inc

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