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8085 Articles
Page 20 of 36
Program counter (PC) in 8085 Microprocessor
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 MoreRunning 8085 program in single-step mode
Running the program in Single-Step Mode:The single step mode is very useful for finding our program which has not yielded the desired outcomes after being executed in a single burst. We use it for program debugging. Similarly, like the operation to be executed singly ‘S’ is typed at the ‘>’ prompt. We can notice clearly that the change of address occurs after S. The given system clearly prompts which is stated below:The address of starting is: xxxx - yy/where the memory address is xxxx and the content of the located memory is yy which allows for responding the user ...
Read MoreMultiple memory address range in 8085 Microprocessor
Suppose we have the chip select circuit as shown in the below figure, then what is the address range for the RAM?Fig. Chip selection that results in multiple address range.A15 and A14 pins are used for the selection of Random Access Memory, and pins ranging from A10 to A0 are used for the selection of location in RAM. But the value of the pins A13, A12 and A11 have non-dependent value. They play no role for selection of chip or location on RANDOM ACCESS MEMORY. Hence they are termed as don't cares and called x for more signification.We have eight ...
Read MoreInstruction register (IR) in 8085 Microprocessor
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 MoreWorking of 74138 decoder IC
Let’s take an Integrated Circuit decoder. We take the popular 3 to 8 decoder Integrated Circuit 74138. The Integrated Circuit is of 16 pins.We have three input pins which are actively in high state and are classified as I2, I1 and I0. The outputs are actively in low state and are eight in number and are classified as O7*, O6*, …, O0*. A power supply of +5 V DC is needed by the chip and is Grounded. ...
Read MoreW and Z registers in 8085 Microprocessor
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 MoreDecimal addition in 8085 Microprocessor
In a digital computer, everything is represented using 0s and 1s only. For example, instruction will have a code using only 0s and 1s. Data is also represented using 0s and 1s. Data can be of different types like unsigned numbers, signed numbers, floating point numbers, binary coded decimal (BCD) numbers, etc. Thus, a series of 0s and 1s will acquire a value based on the interpretation. For decimal addition, we are having a very important and common instruction DAD. Let us discuss more on that instruction now.In spite of the fact that 8085 is an 8-bit microprocessor, but there ...
Read MoreMultiplexer/demultiplexer in 8085 Microprocessor
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 MoreTiming and control unit in 8085 Microprocessor
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 MoreAddress/data buffers in 8085 Microprocessor
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 ...
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