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Instruction type SBI d8 in 8085 Microprocessor
In 8085 Instruction set, SBI is a mnemonic that stands for “Subtract with Borrow Immediate from Accumulator” and here d8 stands for any 8-bit data as operand. This instruction is used to subtract 8-bit immediate data from the Accumulator along with the carry (borrow) value. The result of subtraction will be stored in the Accumulator. As this is an arithmetic instruction, so the flags are affected based on the result produced. It occupies 2 consecutive Bytes in memory.
| Mnemonics, Operand | Opcode(in HEX) | Bytes |
|---|---|---|
| SBI Data | DE | 2 |
Let us consider SBI 13H as a sample instruction falling in this category. It is a 2-Byte instruction. Let us consider the initial content of Accumulator is 44H. The Cy bit has been set. So 13H will get deducted from Accumulator’s content 44H along with carry bit. The internal calculations have been shown below
The result of execution of this instruction has been depicted in the following tracing table −
| Before | After | |
|---|---|---|
(A) |
44H | 30H |
(F) |
Cy=1, other flag bits=any value | Cy=0, AC=1,S=0,P=1,Z=0 |
Cy=0 will indicate that the result is positive.
| Address | Hex Codes | Mnemonic | Comment |
|---|---|---|---|
| 2003 | DE | SBI 13H | A register = A register – 13H – 1 |
| 2004 | 13H | Operand |
Here is the timing diagram for SBI 13H instruction execution.
Summary − So this instruction SBI 13H requires 2-Bytes, 2 Machine Cycles (Opcode Fetch, Memory Read) and 7 T-States for execution as shown in the timing diagram.
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