ht82k70e-l Holtek Semiconductor Inc., ht82k70e-l Datasheet - Page 7

• Manufacturer Part Number: ht82k70e-l
• Description: I/o Type 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

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. 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 writeable 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.
Note:
Rev. 1.00
Initial Reset
INT Interrupt
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
SPI Interrupt
Skip
Loading PCL
Jump, Call Branch
Return from Subroutine
PC12~PC8: Current Program Counter bits
#12~#0: Instruction code address bits
For the HT82K70E-L, the Program Counter Bits is 12 bits wide, the b12 column in the table is not applicable
For the HT82K76E-L, the Program Counter Bits is 13 bits wide, i.e. from b12 ~ b0
Mode
PC12 PC11 PC10
b12
S12
#12
0
0
0
0
0
S11
b11
#11
0
0
0
0
0
b10
S10
#10
0
0
0
0
0
Program Counter
PC9
S9
b9
#9
0
0
0
0
0
7
PC8
S8
b8
#8
0
0
0
0
0
Stack
This is a special part of the memory which is used to
save the contents of the Program Counter only. The
stack has 8 levels and is neither part of the data nor part
of the program space, and is neither readable nor
writeable. The activated level is indexed by the Stack
Pointer, SP, and is neither readable nor writeable. At a
subroutine call or interrupt acknowledge signal, the con-
tents of the Program Counter are pushed onto the stack.
At the end of a subroutine or an interrupt routine, sig-
naled 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.
@7~@0: PCL bits
S12~S0: Stack register bits
Program Counter Bits
Program Counter + 2
@7
S7
b7
#7
0
0
0
0
0
@6
S6
b6
#6
0
0
0
0
0
HT82K70E-L/HT82K76E-L
@5
S5
b5
#5
0
0
0
0
0
@4
S4
b4
#4
0
0
0
0
1
@3
b3
S3
#3
0
0
1
1
0
September 15, 2009
@2
b2
S2
#2
0
1
0
1
0
@1
b1
S1
#1
0
0
0
0
0
@0
b0
S0
#0
0
0
0
0
0