HT56R668 datasheet(15/104 Pages) HOLTEK

15 / 104 page

HT56R67/HT56R668/HT56C668/HT56R678/HT56C678/HT56R688

Rev. 1.20

February 22, 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

b15

b14

b13

b12

b11

b10

Initial Reset

000000

0000000000

External Interrupt 0

000000

0000000100

External Interrupt 1

000000

0000001000

Timer/Event Counter 0 Overflow

000000

0000001100

Timer/Event Counter 1 Overflow

000000

0000010000

SPI/I

2C Interrupt

000000

0000010100

Multi-Function Interrupt

000000

0000011000

Skip

Program Counter + 2

Loading PCL

PC15 PC14 PC13 PC12 PC11 PC10 PC9 PC8 @7 @6 @5 @4 @3 @2 @1 @0

Jump, Call Branch

BP.7

BP.6

BP.5

#12

#11

#10

Return from Subroutine

S15

S14

S13

S12

S11

S10

Program Counter

Note:

PC15~PC8: Current Program Counter bits

@7~@0: PCL bits

#12~#0: Instruction code address bits

S15~S0: Stack register bits

For the HT56R688, the Program Counter is 16 bits wide, i.e. from b15~b0.

For the HT56R67/HT56R678/HT56C678, the Program Counter is 15 bits wide, i.e. from b14~b0.

For the HT56R668/HT56C668, the Program Counter is 14 bits wide, i.e. from b13~b0, therefore the b12

column in the table is not applicable.

BP.7, BP.6, BP.5: Bank pointer bits

1 3 1 2

8 7

P r o g r a m C o u n t e r

B P

. 5

B a n k P o i n t e r ( B P )

B P

. 6

1 4

B P

. 7

1 5

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