Specifications
Chapter 2 - Microcontroller PIC16F84
Instruction cycle consists of cycles Q1, Q2, Q3 and Q4. Cycles of calling and executing instructions
are connected in such a way that in order to make a call, one instruction cycle is needed, and one
more is needed for decoding and execution. However, due to pipelining, each instruction is
effectively executed in one cycle. If instruction causes a change on program counter, and PC
doesn't point to the following but to some other address (which can be the case with jumps or
with calling subprograms), two cycles are needed for executing an instruction. This is so because
instruction must be processed again, but this time from the right address. Cycle of calling begins
with Q1 clock, by writing into instruction register (IR). Decoding and executing begins with Q2, Q3
and Q4 clocks.
TCY0 reads in instruction MOVLW 55h (it doesn't matter to us what instruction was executed,
because there is no rectangle pictured on the bottom).
TCY1 executes instruction MOVLW 55h and reads in MOVWF PORTB.
TCY2 executes MOVWF PORTB and reads in CALL SUB_1.
TCY3 executes a call of a subprogram CALL SUB_1, and reads in instruction BSF PORTA, BIT3. As
this instruction is not the one we need, or is not the first instruction of a subprogram SUB_1
whose execution is next in order, instruction must be read in again. This is a good example of an
instruction needing more than one cycle.
TCY4 instruction cycle is totally used up for reading in the first instruction from a subprogram at
address SUB_1.
TCY5 executes the first instruction from a subprogram SUB_1 and reads in the next one.
Pin description
PIC16F84 has a total of 18 pins. It is most frequently found in a DIP18 type of case but can also
be found in SMD case which is smaller from a DIP. DIP is an abbreviation for Dual In Package.
SMD is an abbreviation for Surface Mount Devices suggesting that holes for pins to go through
when mounting, aren't necessary in soldering this type of a component.
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