HT45R37 datasheet(10/100 Pages) HOLTEK

10 / 100 page

HT45R37

Rev. 1.10

January 29, 2010

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. It must be

noted that only the lower 8 bits, known as the Program

Counter Low Register, are directly addressable.

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 pro-

gram 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 loca-

tions. When such program jumps are executed it should

also be noted that a dummy cycle will be inserted.

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 0

000000000100

External Interrupt 1

000000001000

Timer/Event Counter 0 Overflow

000000001100

Timer/Event Counter 1 Overflow

000000010000

SPI/I

2C Interrupt

000000010100

C/R to F Converter Interrupt

000000010100

Time Base Interrupt

000000011000

RTC Interrupt

000000011000

A/D Converter Interrupt

000000011000

External Peripheral Interrupt

000000011000

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

HT45R37 Datasheet(PDF) 10 Page - Holtek Semiconductor Inc

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