Describe the branch instructions associated with CCR bits. 

 

In CCR, branch instructions cause program flow to change when specific condition is met.

Branches are helpful for:

• Infinite execution of a program
• Conditional operations
• Loops
• and to add time delays

A program branch can be taken when a specific bit in the CCR register is in a specific state (0 or 1). We use:

• Unsigned branches : When a comparison of unsigned quantities result in a specific combination of CCR bits
• Signed branches : When comparison of signed quantities result in a specific combination of CCR bits

Some branch based commands:

• BCC : Branch if carry clear (C flag=0)
• BCS: Branch if carry set (C flag=1)
• BMI: Branch if minus (N flag =1)
• BVS: Branch if overflow set (V flag=1)

Example: Assume X contains $50 and Y contains $100

Loop:

Ldaa 1,x+

Ldab 1,y+

Aba

Bcs Loop1 ; Branch if the carry bit is 1

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Bra Loop

Loop1:

Staa $100