Subject: Microprocessor Microcontroller MCS-51: Week 7: Branch Instructions

1. MICROCONTROLLER
MCS-51:
BRANCH INSTRUCTION
Arkhom JODTANG
Civil Aviation Training Center

2. Branch Instruction
Contents
 Flowchart
 Branch Instructions
 Design program
2

3. Flowchart
 A flowchart is a diagrammatic representation that
illustrates the sequence of operations to be
performed to get the solution of a problem.
 Flowcharts are generally drawn in the early stages
of formulating computer solutions.
 Flowcharts facilitate communication between
programmers and business people.
 These flowcharts play a vital role in the
programming of a problem and are quite helpful in
understanding the logic of complicated and
lengthy problems.
3

4. Flowchart Symbols
 Terminator
 The start or end of program flow
 Initial / Preparation
 Setting a value at the beginning of the
process or initialize the routine
 Process
 Any kind of processing function, such as a
variable assignment or mathematical
operation.
 Predefined Process
 A named process, such as a subroutine, a
module, Procedure or Function.
Start
4

5. Flowchart Symbols
Condition  Decision
 Select flow direction from condition
 Connector
 Jumping destination
 Flow line
connect the flowchart symbols and
show the sequence of operations
during the program execution.
True
False
5

6. Flowchart Sample
Start
A = 30H
Process
End
MainLoop:
A = 0
6
Jump to MainLoop

7.  Labels are destination point that program (flowline) able to join.
 One program able to contain unlimited number of labels.
 Name of Labels follow the standard identifier rule
 Start with Letter
 Only Letter, Number and Underscore
 Case sensitive
 All label follow by colons
 Labels name, such as
 Loop:
 Delay:
 Multipli4X4Bytes:
 CheckOnes:
Label (Relative address)
MainLoop:
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8. Sample of Branch Instruction
(Unconditional Jump)
ORG 0H
MOV R1,#40H
Loop:
MOV @R1,#22H
INC R1
JMP Loop
END
8

9. Sample of Branch Instruction
(Conditional Jump)
ORG 0H
MOV R1,#40H
Loop:
MOV @R1,#11H
INC R1
CJNE R1, #50H, Loop
END
9

10. JMP rel., SJMP rel.
 Jump to specified relative address
 -128 to +127 locations (Short Jump)
 No condition.
 Sample
 SJMP NO_Task
 Jump to label name is No_Task
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11. AJMP adr11
 Jump to any specific location
 Long distance. (211 = 2kByte long)
 No condition.
 Sample
 AJMP Loop3
 Jump to label name is Loop3
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12. LJMP adr16
 Jump to any specific location
 Long distance. (216 = 64kByte long)
 No condition.
 3 Bytes instruction
 4 Machine cycles
 Sample
 LJMP Program5
 Jump to label name is Program5
12

13. JC rel
 Condition: Jump if carry bit is set
 Jump to specific destination
 Short Jump
 3 Machine cycles
 Sample
 JC Store_It
 If Carry bit = Set, Jump to label “Store_It”
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14. JNC rel
 Condition: Jump if carry bit is clear
 Jump to specific destination
 Short Jump
 3 Machine cycles
 Sample
 JNC EasyTask
 If Carry = 0, Jump to EasyTask
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15. JNC Sample
 Example 3: Program to make summation of Timer0 and Timer1 registers.
Store the result in R0 (Highest Byte), R1 and R2 (Lowest Byte).
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 To assign value of
Carry Flag to R0
ORG 00H
MOV R0, #00H
JNC CarryIsZero
MOV R0,#01H
CarryIsZero:
END
Timer0
Timer1
+
TL0TH0
R1 R2R0

16. Bit
16
 Any bit in memory
 Carry
 Acc.0
 PSW.4
 20h.0
 00h
 7Fh
 P3.3
Addres
s
.7 .6 .5 .4 .3 .2 .1 .0 Name
19h
20h 07 06 05 04 03 02 01 00
21h 0F 0E 0D 0C 0B 0A 09 08
2Fh 7F 7E 7D 7C 7B 7A 79 78

17. JB bit, rel
 Condition: Jump if addressed bit is set
 Jump to specific destination
 Short Jump
 2 Machine cycles
 Sample
 JB 00h, EasyTask
 If bit address 00h is set, Jump to label EasyTask:
 JB P3.4, NOTPressedS4
 If bit P3.4 = set. Jump to label PressedS4
17

18. JNB bit, rel
 Condition: Jump if addressed bit is clear
 Jump to specific destination
 Short Jump
 2 Machine cycles
 Sample
 JNB 00h, EasyTask
 If bit address 00h is clear, Jump to label EasyTask:
18

19. JBC bit, rel
 Condition: Jump if addressed bit is set
 Clear bit
 Jump to specific destination
 Short Jump
 4 Machine cycles
 Sample
 JBC 00h, EasyTask
 If bit address 00h is set, jump to label EasyTask:, Clear bit
00h
 JBC PSW.4, EasyTask
 If bit address PSW.4 is set, jump to label EasyTask:, Clear
bit PSW.4
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20. JZ rel
 Condition: Jump if Acc equal to zero
 Jump to specific destination
 Short Jump
 3 Machine cycles
 Sample
 JZ EmptyNow
 If ACC = 0, Jump to label EmptyNow:
20

21. JNZ rel
 Condition: Jump if Acc not equal zero
 Jump to specific destination
 Short Jump
 3 Machine cycles
 Sample
 JNZ SomeValue
 If ACC > 0, Jump to label Somevalue:
21

22. CJNE A, Rx, rel
 Condition: Jump if Acc not equal to Rx
 Jump to specific destination
 Short Jump
 4 Machine cycles
 Effect to carry flag
 Sample
 CJNE A, 30h, Loop2
 If ACC ≠ 30h, Jump to label Loop2:
22

23. CJNE A, #X, rel
 Condition: Jump if Acc not equal to #X
 Jump to specific destination
 Short Jump
 4 Machine cycles
 Sample
 CJNE A, #3Eh, Loop3
 If ACC ≠ #30h, Jump to label Loop3:
23

24. CJNE Rn, #X, rel
 Condition: Jump if Rn not equal to #X
 Jump to specific destination
 Short Jump
 4 Machine cycles
 Sample
 CJNE R4, #40h, Loop4
 If R4 ≠ #40h, Jump to label Loop4:
24

25. CJNE @Ri, #X, rel
 Condition: Jump if register addressed by Ri
not equal to #X
 Jump to specific destination
 Short Jump
 4 Machine cycles
 Sample
 CJNE @R0, #0E0h, Loop5
 If register which is addressed by R0 ≠ #E0h, Jump to
label Loop5:
25

26. Comparison Conditional tips
Most of conditional jumps are Not Equal Condition
JZ ( A = 0 ) JNZ
CJNE A, Rx, rel
CJNE A, #X, rel
CJNE Rn, #X, rel
DJNZ Rn, rel

27. Example 1
 Write program to fill the memory area
address 30h to 4Fh with counting number
start from 1H
27

28. Example 1: Result needed
 Write program to fill the memory area
address 30h to 4Fh with counting number
start from 1H
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29. Example 1: Solution
 Write program to
fill the memory
area address 30h
to 4Fh with
counting number
start from 1H
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30. CJNE (Homework)
 Write program to fill the memory area address 30h to 6Fh
with Decimal (BCD) counting number start from 0H
 The code must less than 15 line of assembly code
30

31. DJNZ Rn, rel
 Process: Decrease Rn by one, then
 Condition: Jump if Rn not equal to zero
 Jump to specific destination
 Short Jump
 3 Machine cycles
 Sample
 DJNZ R5, Loop6
 Decrease R5 then check, If R5 ≠ 0, Jump to label
Loop6:
31

32. DJNZ Rx, rel
 Process: Decrease Rx by one, then
 Condition: Jump if Rx not equal to zero
 Jump to specific destination
 Short Jump
 4 Machine cycles
 Sample
 DJNZ R5, Loop6
 Decrease R5 then check, If R5 ≠ 0, Jump to label
Loop6:
32

33. DJNZ (Sample)
 ; DJNZ is very convenion for
 ; specified number of turn for
some process.
 ORG 0H
 MOV R5,#10D
 Loop:
 ; Process here
 DJNZ R5, Loop
 END
33
Start
R5 =10D
Process
End
Loop:
DJNZ R5, Loop