HLT instruction in 8085

Microprocessor8085

In 8085 Instruction set, HLT is the mnemonic which stands for ‘Halt the microprocessor’ instruction. It is having a size of 1-Byte instruction. Using these particular instructions, as 8085 enters into the halt state, so we can put the8085 from further processing of next instructions. This is indicated by S1 and S0 control signals. During the halt, S1 and S0 output signals will become 0 0. 

Mnemonics, Operand
Opcode(in HEX)
Bytes
HLT
76
1


The 8085 comes out of the Halt state when a valid interrupt occurs. In such a case, it executes the corresponding interrupt service subroutine depending upon the interrupt number and then it continues with the instruction after the HLT instruction. So it will not effectively enter into the halt state in that situation.

However, in most programs, the HLT instruction is used for terminating the program. Also, activation of reset in* causes 8085 to come out of Halt state.

Address
Hex Codes
Mnemonic
Comment
2002
76
HLT
Entering 8085 in the HALT state


The timing diagram against this instruction HLT execution is as follows –

Summary − So this instruction HLT requires 1-Byte, 2-Machine Cycles (Opcode Fetch, Bus Idle Cycle) and5 T-States for execution as shown in the timing diagram.

raja
Published on 28-Dec-2018 14:26:51
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