If SS = 3000 H and SP = 2000 H in 8086 microprocessor, in which memory addresses the contents of BL and BH are stored respectively, when PUSH BX instruction is executed.
31FFEH, 31FFFH
The problem involves understanding how the stack operations work in the 8086 microprocessor. Specifically, we are asked to determine the memory addresses where the contents of the BL and BH registers are stored when the PUSH BX instruction is executed.
Understanding PUSH Operation
When a PUSH instruction is executed on a register, the contents of the register are pushed onto the stack. In an 8086 microprocessor, the stack grows downward (from higher to lower memory addresses). The stack segment (SS) register points to segment, and the stack pointer (SP) register contains the offset within that segment.
Calculating Initial Address
- The segment address = \(SS \times 16 = 3000 \, H \times 16 = 30000 \, H\).
- The initial stack pointer (SP) = 2000H.
Hence, the initial stack top address = \(30000 \, H + 2000 \, H = 32000 \, H\).
Effect of PUSH BX
- The
PUSHoperation first decrements the SP by 2 to make space for the register contents. - The contents of the higher byte (BH) are pushed to the memory address where SP points to, then SP is decremented again to push the lower byte (BL).
Determining New SP and Addresses
- After the first decrement, SP = 1FFEH.
- The content of BL is stored at address \(32000 \, H - 02 = 31FFE \, H\).
- Next, the SP is decremented again to 1FFCH (since PUSH decrements SP by two bytes for the next byte).
- The content of BH is stored at address \(32000 \, H - 04 = 31FFF \, H\).
Conclusion
Thus, the addresses where BL and BH are stored respectively after the PUSH BX operation are 31FFEH and 31FFFH. Hence, the correct answer is:
31FFEH, 31FFFH
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