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


44H 30H


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.

Published on 04-Dec-2018 08:41:56