Branch call and time delay functions are introduced in this slide set. This is a part of the introduction to embedded systems.

1. Branch, call and time delay
loop

2. Looping in PIC
• Method 1: repeat the operation again and again

3. Looping in PIC
• DECFSZ (decrement filReg skip zero)

4. Looping in PIC
• BNZ (Branch if not zero) [pic 18 family]

5. Loop inside a loop (nested loop)

6. Branch (jump) instructions

7. Calculating the short branch address
• Target address = 2nd byte of instruction X 2 +PC
• Second byte value  -127 to +128 (2s complement method)
• Verify the calculation of backward jump
FDH = -3
-3 X 2 =-6
-6 + 0000CH = 06H
6H  address of the label again

8. Unconditional branch instruction
• There are two unconditional branches in PIC 18
• GOTO
• BRA
• GOTO
• This can go to any memory location in 2M address space
• 4 byte (32 bits)  12(opcode) + 20(address of the target location)
• BRA (branch)
• 2 byte (16 bits)  5(opcode) + 11(relative address)[forward + backward]
• -1024 to +1023

9. Unconditional branch instruction
• GOTO instruction (more)

10. Unconditional branch instruction
• BRA (more)
• GOTO itself

11. CALL instruction
• This is used to call subroutine
• PIC 18
• CALL (long call)
• RCALL (relative call)
• A stack is used
• PIC 18 has 5-bit stack pointer
32 locations (actually 31)

12. CALL instruction

13. CALL instruction
• RCALL
• 2 byte instruction
• Subroutine must be within 2K (only 11 bits, 5bits for opcode)
(CALL  2M space)
• Can save ROM space

14. Time delay and instruction pipeline
• Two factors that can affect the accuracy of the delay
• The crystal frequency
• The PIC design: Harvard architecture, RISC architecture features and
pipelining
• Pipelining

15. Instruction cycle time for the PIC
• In PIC 18  one instruction cycle  4 oscillator periods.

16. Instruction cycle time for the PIC

17. Instruction cycle time for the PIC

18. Instruction cycle time for the PIC
• Solution

19. Delay calculation

20. Delay calculation
• solution

21. Delay calculation (loop inside a loop)

22. Delay calculation (loop inside a loop)
• solution

23. Delay calculation

24. Delay calculation

25. PIC multistage execution pipeline
4 clock periods
of the oscillator

26. Summary