Address and data buffers are used for bidirectional data transfer. They perform the unidirectional data transfer when they send out the Least Significant Byte of the address. These buffers are only used for increasing the driving capacity of the current. Through the internal bus data goes to the buffers. The Least Significant Byte of the address goes to the buffers from the internal address latch to the other.Hence the address or data are sent out on the address ranging from AD7 to AD0 can drive every external chips, like chips of RAM, chips of EPROM, and other peripheral chips meant for ... Read More

Let us consider the instruction to be executed as “MOV A, C”. Here in this case the value of 8 bit in the register C must be moved to the register. The given set of registers namely B, C, D, E, H, and L must be connected to the internal bus by means of a multiplexer (many input but only one output) or demultiplexer the reverse of multiplexer. The register meant to carry the work selects the specific unit and sends the appropriate code to the multiplexer such that the contents of register C are sent out to the multiplexer ... Read More

Temporary register is also an 8-bit register which the programmer can’t access at all. It is temporarily stored inside 8085 microprocessor which is 8 bit operand to the instruction set. For example, when the fetching of instructions “MVI M, 34H” is done the instruction register IR register will receive the opcode for MVI M, and the Temp register receives 34H.The operations of arithmetic and logical sequence carried out involves two operands, among which one is operand is provided by the accumulator, and the other operand is provided by the Temp register. For example, in the addition process the instruction to ... Read More

We use Timing and Controlling unit in 8085 for the generation of timing signals and the signals to control. All the operations and functions both interior and exterior of a microprocessor are controlled by this unit. X2 and CLK output pins: To do or rather perform the operations of timing in the microcomputer system, we have a generator called clock generator in the CU of 8085. Other than the quartz crystal the complete circuit of the oscillator is within the chip. The two pins namely X1 and X2 are taken out from the chip to give the connection to the ... Read More

The main differences between a JMP instruction and a CALL instruction is as follows –If a JMP instruction is executed, we jump to the destination location, and the execution carries on from there, without bothering to come back later to the instruction after the JMP. On the other hand, if a CALL instruction is executed, we jump to the subroutine, and the execution carries on from there till the RET instruction is executed in the subroutine, and then we come back to the instruction after the CALL in the main program.The address of the next instruction after the CALL instruction ... Read More

To define Temporary Register, we can mention that it is an 8-bit non-programmable resister used to hold data during an arithmetic and logic operation (temporary resister is used to hold intermediate result). The result is stored in the accumulator, and the flags (flip-flops) are set or reset according to the result of the operation.W and Z are two 8-bit temporary registers of 8085 microprocessor, which is not accessible to the user. They are exclusively used for the internal operation by the microprocessor. These registers are used either to store 8-bit of information in each W and Z registers or a ... Read More

IR (Instruction Register) is a special purpose register, which is used to receive the 8-bit opcode portion of an instruction. It is not accessible to the programmer. What it means is that there are no instructions by which the programmer can load it with values of his choice. For example, instructions like ‘MOV IR, D’ or ‘MVI IR, 45H’ are not present in the instruction set of 8085. Thus, IR register is not shown in the programmer's view of 8085.Let us consider one example. First of all, PC is loaded with the value 8000H. This is done by typing the ... Read More

PC is a 16-bit register. It contains a memory address. PC contains that very memory address from where the next instruction is to be fetched for execution. Suppose the PC contents are 8000H, then it means that the 8085 Desires to fetch the instruction Byte at 8000H. After fetching the Byte at 8000H, the PC is automatically incremented by 1. This way 8085 becomes ready to fetch the next Byte of the instruction (in case instruction fetch is incomplete), or fetch the next opcode (in case instruction fetch is over).So in this example, first of all PC is loaded with ... Read More

Reading from the StackLet us consider that SP contents the address FC78H, and we want to read information from a stack location. In this case, we are not interested in reading from a location whose address is less than the memory address present in SP. This is because 8085 interprets them as useless information. For example, there is no point in reading useless information from memory location FC75H.SP interprets that, memory locations FC78H, FC79H, ..., FFFFH are all interpreted by 8085 to have useful information. To read from Stack, the instruction is POP in 8085 microprocessor instruction set. Here we ... Read More

The stack is a LIFO (last in, first out) data structure implemented in the RAM area and is used to store addresses and data when the microprocessor branches to a subroutine. Then the return address used to get pushed on this stack. Also to swap values of two registers and register pairs we use the stack as well.In the programmer‘s view of 8085, only the general purpose registers A, B, C, D, E, H, and L, and the Flags registers were discussed so far. But in the complete programmer’s view of 8085, there are two more special purpose registers, each ... Read More