Rev. 1.60
36
August 20, 2019
Rev. 1.60
37
August 20, 2019
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
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. For the device whose memory capacity is greater than 8K
words the Program Memory address may be located in a certain program memory bank which is
selected by the program memory bank pointer bit, PBP0 or PBP1. Only the lower 8 bits, known as
the Program Counter Low Register, are directly addressable by the application program.
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.
Device
Program Counter
High Byte
Low Byte (PCL)
BS66F340
PC11~PC8
PC7~PC0
BS66F350
PC12~PC8
PC7~PC0
BS66F360
PBP0, PC12~PC8
PC7~PC0
BS66F370 PBP0, PBP1, PC12~PC8
PC7~PC0
Program Counter
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. Manipulating the PCL register may cause program branching, so an extra cycle is
needed to pre-fetch.