HT46R064D/065D/066D
Enhanced A/D Type 8-Bit OTP MCU with LED Driver
For instructions involving branches, such as jump or call instructions, two instruction cycles are
required to complete instruction execution. An extra cycle is required as the program takes one cycle to
first obtain the actual jump or call address and then another cycle to actually execute the branch. The
requirement for this extra cycle should be taken into account by programmers in timing sensitive
applications.
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 ²JMP² or ²CALL² 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
HT46R064D
HT46R065D
HT46R066D
PC9,PC8
PC10~PC8
PCL7~PCL0
PC11~PC8
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 loca-
tions. 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 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
14
January 12, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
