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Microprocessor Articles
Page 4 of 42
Overview of the working of 8259
The interrupt requests are accepted by 8259 from many interrupting devices IR0 to IR7 pins. After that, it identifies the highest priority interrupt request from those inputs that are already active. To configure the 8259 for fixed priority mode of operation, among them IR0 has the highest and IR7 has the lowest priority. If the inputs IR2, IR4, and IR6 are active, thenIR2 has the highest priority interrupt request among the active requests than the other. The details of the interrupt requests those are active are stored in the Interrupt Request Register (IRR).By loading the Interrupt Mask Register (IMR), it ...
Read MoreArchitecture of 8259
8259 Microprocessor is architected in a unique style. It can program by means of some interrupts conditions by means of level or interrupt level often called edge-triggered interrupt level. Masking is done to individual interrupt bits. As the number of 8259 increases interrupt pins up to 64 can be obtained. There are 3 registers 8259 contains along with one priority resolver(PR). They are as follows −Interrupt Request Register(IIR) − It stores the bits who requests the interrupt.Interrupt service register(ISR) − It stores the currently interrupt levels.Interrupt Mask Register(IMR) − Stores the interrupt levels to be masked.PriorityResolver(PR) − Set the priority of ...
Read MorePins of 8259
Intel 8259 is designed as a 28-pin-programmable IC available as a package named DIP (Dual inline package). Its physical and functional pin diagrams are indicated below.PIN NameDescription and PurposesVcc and GndIt is the Power supply and ground pins. +5V power supply isused in this chip.D7-0For communication with the processor, there are Eight bi-directional data pins.RD*It is active low-input pin activated by the processor to read the information status from the 8259.WR*It is an active low-input pin which is activated by the processor to write the control information to 8259.CS*For selecting the chip it is used an active low input pin.A0An ...
Read MoreInstruction to complement Accumulator in 8085 Microprocessor
In 8085 Instruction set, logical type there is one complement instruction with the mnemonic CMA. It actually stands for “CoMplement the Accumulator”. It performs1's complement operation on the current contents of Accumulator, and the result is stored back in the Accumulator replacing its previous contents. It is to be noted that, there are no other instructions tocomplement any other register’s contents. Though it is a logicaltype of instruction, Flag bits are not affected by the execution of this instruction. It occupies only 1 Byte in memory. Mnemonics, OperandOpcode(in HEX)BytesCMA2F1Let us suppose that example, the initial content of Accumulator is AAH i.e. ...
Read MoreInstructions to complement/set Cy flag in 8085 Microprocessor
In 8085 Instruction set, there are two instructions to control the Cy flag bit content. Thesemnemonics are STC and CMC. Both are 1-Byteinstructions. There hex codes are given in the following table – Mnemonics, OperandOpcode(in HEX)BytesSTC371CMC3F1Using STC instruction we can set the Cy flag bit to 1 irrespective of itsprevious value. And using CMC instruction we can complement the current value of the Cy fag bit andresult will update the current Cy flag bit value. Here STC stands for “SeT the Carry flag” and CMC stands for “CoMplement the Carry flag”. Note that, there isno dedicated instruction in 8085 instruction set ...
Read MoreInstructions to perform compare operation in 8085 Microprocessor
In 8085 Instruction set, we are having a set of instructions to perform compare operation where we shall compare two operands, and which will affect the status flags values depending on the result of the comparison. In this operation, 8085 imposes the restriction that one of the operands must be in the Accumulator. The other operand can be one of the following –ClassificationsExamplesThe other operand can be kept in 8-bit immediate data in the instruction.CPI 43HCPI FFHThe other 8-bit operand can be kept in a memory location and whose memory address will be pointed by HL register pair.CMP MThe other ...
Read MoreInstructions to rotate Accumulator in 8085 Microprocessor
In 8085 Instruction set, there a set of instructions which can Accumulator contents left orright. It is to be noted here that rotate operation can be performedonly on Accumulator contents. These instructions set is listed below– Mnemonics, OperandOpcode(in HEX)BytesRAL171RAR1F1RLC071RRC0F1Mnemonic RLC stands for “Rotate Left Accumulator”. It rotates the Accumulator contents to the left by 1-bit position. The following Fig. shows the operation explicitly – In this fig. it has been depicted that the mostsignificant bit of the Accumulator will come out and left rotate willcreate an empty space at the least significant bit place and thiscome out bit will be copied at ...
Read MoreConditional and Unconditional JUMP instructions in 8085 Microprocessor
In 8085 Instruction set, there are a set of jump instructions, which can transfer program control to a certain memory location. So after these branching mnemonics we shall have to mention 16-bit target address of the location. These jump instructions can be divided into two categories– Unconditional jump instructions andConditional jump instructionsUnder unconditional jump instructions there is only one mnemonic i.e. JUMP. But under conditional Jump instructions we are having 8 different mnemonics. We know that there are 5 flag bits in 8085 Flag register. They are S, Z, P, Cy, AC. Out of them only on AC flag bit, there ...
Read MoreJump if carry (JC) in 8085 Microprocessor
In 8085 Instruction set, we are having one mnemonic JC a16, which stands for “Jump if Carry” and “a16” stands for any 16-bit address. This instruction is used to jump to the address a16 as provided in the instruction. But as it is a conditional jump so it will happen if and only if the present carry flag value is 1.If carry flag value is 0, program flow continues sequentially. It is a 3-Byte instruction.Mnemonics, OperandOpcode(in HEX)BytesJC LabelDA3Let us consider one example of this instruction type JC 4000H. It is a 3-Byte instruction. The result of execution of this instruction ...
Read MoreUnconditional call and return instructions in 8085 Microprocessor
Sometimes in 8085assembly language coding, we require to repeat a certain program segment for multiple times. In those situations, we can define sub-routines. In those subroutines, we can enclose our repeatedly reusable Instruction set or code. And then as when required we shall call those sub-routines accordingly. Sub-routines can also be called as procedures.Whenever the instructions in a subroutine are required to be executed, we branch program control to the subroutine using th CALL instruction. CALL is a 3-Byte instruction, with 1 Byte for the opcode, and 2 Bytes for the address of the subroutine. CALL mnemonics stands for “call ...
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