Chapter 04 - The Von Neumann Model

# Status bits n set if result is negative else reset z

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Status Bits N: Set if result is negative, else reset Z: Set if result is zero, else reset C: Set if there is a carry, else reset V: Set if an arithmetic overflow, else reset Example ADD.W @R13+,10(R13) ; ADD LSDs ADDC.W @R13+,10(R13) ; ADD 2/carry Assembly Instructions

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BYU CS/ECEn 124 Chapter 4 - The Von Neumann Model 21 AND Source to Destination AND Source AND destination Syntax AND{.W or .B} src,dst Operation src .AND. dst −> dst Description The source operand and the destination operand are logically ANDed. The result is placed into the destination. Status Bits N: Set if result MSB is set, else reset Z: Set if result is zero, else reset C: Set if result is not zero, else reset V: Reset Example MOV #0AA55h,R5 ; Load mask AND R5,TOM ; mask M(TOM) JZ TONI Assembly Instructions
BYU CS/ECEn 124 Chapter 4 - The Von Neumann Model 22 Clear Bits in Destination BIC Clear bits in destination Syntax BIC{.W or .B} src,dst Operation .NOT.src .AND. dst −> dst Description The inverted source operand and the destination operand are logically ANDed. The result is placed into the destination. The source operand is not affected. Status Bits Status bits are not affected. Example BIC.W #0FC00h,LEO ; Clear 6 MSBs BIC.B #0F8h,LEO ; Clear 5 MSBs Assembly Instructions

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BYU CS/ECEn 124 Chapter 4 - The Von Neumann Model 23 Set Bits in Destination BIS Set bits in destination Syntax BIS{.W or .B} src,dst Operation src .OR. dst −> dst Description The source operand and the destination operand are logically ORed. The result is placed into the destination. The source operand is not affected. Status Bits Status bits are not affected. Example BIS.W #003Fh,TOM ; set the 6 LSBs BIS.B #0E0h,TOM ; set the 3 MSBs Assembly Instructions
BYU CS/ECEn 124 Chapter 4 - The Von Neumann Model 24 Test Bits in Destination BIT Test bits in destination Syntax BIT{.W or .B} src,dst Operation src .AND. dst Description The source and destination operands are logically ANDed. The result affects only the status bits. The source and destination operands are not affected. Status Bits N: Set if MSB of result is set, else reset Z: Set if result is zero, else reset C: Set if result is not zero, else reset V: Reset Example BIT #0200h,R8 ; bit 9 of R8 set? JNZ TOM ; Y Assembly Instructions

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BYU CS/ECEn 124 Chapter 4 - The Von Neumann Model 25 Subroutine Call CALL Subroutine Syntax CALL dst Operation dst −> tmp dst is evaluated and stored SP − 2 −> SP PC −> @SP PC updated to TOS tmp −> PC dst saved to PC Description A subroutine call is made to an address anywhere in the 64K address space. All addressing modes can be used. The return address (the address of the following instruction) is stored on the stack. The call instruction is a word instruction.
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• Fall '08
• Staff
• Computer Architecture, Central processing unit, von Neumann model, Von Neumann architecture

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