• Instructions operate only on registers
• If you want to add the values stored in two memory locations, you must
  • Load each value in memory into a register
  • Store the result in a memory
• Binary operations take two operands
• The result is stored in the destination (Rd) register

Some popular arithmetic instructions:

• ADD Rd, Rr
  • Rd ← Rd + Rr
• SUB Rd, Rr
  • Rd ← Rd - Rr
• ADC Rd, Rr
  • Rd ← Rd + Rr + C where C is the contents of the carry flag
• SBC Rd, Rr
  • Rd ← Rd - Rr - C

Example of adding two 16-bit numbers:

• Suppose one number is stored in R1:R0 and the other in R3:R2
• We would add these as follows:

  ADD R0, R2
  ADC R1, R3

• The result is stored in R1:R0

• These instructions modify the program counter.
• Jump instructions are sometimes lumped in with the branch instructions since they modify the program counter as well.
• RJMP and all of the branch instructions use relative addressing
• Relative addressing is faster than direct addressing, but it limits how far you can jump.
• The assembler will warn you if you are trying to jump too far (not very common)
• JMP does not use relative addressing and can
• If you want to add the values stored in two memory locations, you must
  • Load each value in memory into a register
  • Store the result in a memory
• Binary operations take two operands
• The result is stored in the destination (Rd) register

Some popular arithmetic instructions:

• RJMP k
  • PC ← PC + k + 1
  • where -2K ⇐ k < 2K
• JMP k
  • PC ← k
  • where 0 ⇐ k < 4M
• BRNE k
  • if(Z==0) PC ← PC + k + 1
  • where -64 ⇐ k < 64
• BREQ k
  • if(Z==1) PC ← PC + k + 1
  • where -64 ⇐ k < 64