Instruction type DCX SP in 8085 Microprocessor

Microprocessor8085

In 8085 Instruction set, DCX SP instruction is used to decrement the SP contents by 1. DCX SP instruction is a special case of DCXrpinstruction which decreases the content of the register pair. This instruction occupies only 1-Byte in memory.

Mnemonics, Operand Opcode(in HEX) Bytes
DCX SP 3B 1

Let us consider that the initial content of SP is 4050H. So after decrement of the content of SP by using DCX SP instruction, SP would have the value 404FH. Here is the required tracing table as below −

Before After

(SP)

4050H 404FH

Address Hex Codes Mnemonic Comment
2003 3B DCX SP SP ←SP - 1

The timing diagram against this instruction DCX SP execution is as follows −

DCX SP

Summary − So this instruction DCX SP requires 1-Byte, 1-Machine Cycle (Opcode Fetch) and 6 T-States for execution as shown in the timing diagram.

raja
Published on 05-Dec-2018 10:50:37
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