PIC Code Execution

How does the CPU executes this simple program? void main() { int i; i = 1; i++; }

Assembly Code MOVLW 01 BCF 03.5 MOVWF 21 INCF 21,F

Machine Code

File Register Map See figure 6-5 in the handout For a complete File Register layout

The 4 Qs Q1 = Instruction Decode Q2 = Fetch Operand Q3 = Process the Data Q4 = Write Result Data See section 4.2, 4.3 in the handout for details

Instruction Pipeline Flow time Cmd1 Cmd2 Cmd3 Flash->Ins RegQ1Q2Q3Q4 Flash->Ins RegQ1Q2Q3Q4 Flash->Ins RegQ1Q2Q3Q4 FetchExecute Q1 = Instruction Decode Q2 = Fetch Operand Q3 = Process the Data Q4 = Write Result Data

Pipeline interruption time Q1 = Instruction Decode Q2 = Fetch Operand Q3 = Process the Data Q4 = Write Result Data Goto 3 Cmd2 Cmd3 Flash->Ins RegQ1Q2Q3Q4 Flash->Ins Reg Q1Q2Q3Q4 FetchExecute

Program Execution Example int i; i=1; 000D: MOVLW E: BCF F: MOVWF i++; 0010: INCF 21,F

Converting Assembly to Machine Code MOVLW 01 BCF 03.5 MOVWF 21 INCF 21,F Look at table 5-1 in the handout for the machine code reference

Program Execution Ex int i; i = 5; 000D: MOVLW E: BCF F: MOVWF do { i--; 0010: DECF 21,F } while (i>0); 0011: MOVF 21,F 0012: BTFSS : GOTO 010