HT46R46 datasheet(9/77 Pages) HOLTEK

9 / 77 page

HT46R46/C46/R47/C47/R48A/C48A/R49

Rev. 1.30

June 5, 2008

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. For the

Cost-Effective A/D Type series of microcontrollers, 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.

Mode

Program Counter Bits

b11

b10

Initial Reset

000000000000

External Interrupt

000000000100

Timer/Event

Counter

Overflow

000000001000

A/D Converter Interrupt

000000001100

Skip

Program Counter + 2

Loading PCL

PC11 PC10

PC9

PC8

Jump, Call Branch

#11

#10

Return from Subroutine

S11

S10

Program Counter

Note:

PC11~PC8: Current Program Counter bits

@7~@0: PCL bits

#11~#0: Instruction code address bits

S11~S0: Stack register bits

For the HT46R49, the Program Counter is 12 bits wide, i.e. from b11~b0.

For the HT46R47 and HT46R48A, the Program Counter is 11 bits wide, i.e. From

b10~b0, therefore the b11 column in the table is not applicable.

For the HT46R46, the Program Counter is 10 bits wide, i.e. from b9~b0, therefore the b11 and

b10 the columns in the table are not applicable.

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