HT46R068B/HT46R069B
Enhanced A/D Type 8-bit OTP MCU
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Instruction Fetching
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. Note that the Program Counter width varies with the
Program Memory capacity depending upon which device is selected. 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 conditional skip instructions, once
the condition has been met, the next instruction, which has already been fetched during the present
instruction execution, is discarded and a dummy cycle takes its place while the correct instruction
is obtained.
Program Counter
DEVICE
Program Counter
High Byte
PCL Register
HT4ꢄR0ꢄ8B
HT4ꢄR0ꢄ9B
PC13~PC8
PC14~PC8
PCL7~PCL0
14 13 1ꢃ
8 7
0
Pꢁogꢁam Coꢀnteꢁ
BP ꢄ BP 5
Bank Pointeꢁ(BP)
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 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 inserted.
The lower byte of the Program Counter is fully accessible 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.
Rev. 1.00
1ꢃ
�anꢀaꢁꢂ ꢃꢄꢅ ꢃ011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
