Microprocessor 8085 Machine Cycle
Microprocessor 8085 Q: Why, in 8085, Opcode fetch have 4 T-States whereas all other machine cycles have only 3 T-States? A: When an instruction is about to be executed, the first machine cycle that is performed by 8085 microprocessor is the opcode fetch machine cycle. Before knowing the opcode fetch machine cycle, we have to know what is actually the opcode is. There are 256 different instructions in 8085 microprocessor. Some of them are near about similar. To distinguish between all the 256 instructions, there are 256 different hexadecimal operational codes that is stored in the 8085 memory. Let an instruction be MVI A,23H is about to be executed. The hexadecimal code for MVI A is 3AH and that is fixed inside the 8085 memory. When the instruction as about to be executed, the programmer or the user will have to give input the 3AH data in the program input. When 8085 reads the input from the user, it first checks whether the input code is actually the opcod...