MACHINE CYCLES AND BUS TIMINGS
MACHINE CYCLES AND BUS TIMINGS The Z80 microprocessor is designed to execute 158 different instruction types. Each instruction has two parts: operation code (known as opcode) and operand. The opcode is a command such as Add, and the operand IS an object to be operated on, such as a byte or the contents of a register. Some instructions are 1-byte instructions. and some are multibyte instructions. To execute an instruction, the Z80 needs to perform various operations such as Memory Read/Write and I/O Read/Write. However, there is no direct relationship between the number of bytes of an instruction and the number of operations the Z80 has to perform. For example, the instruction to send the contents of the accumulator to the output port 10 H ,is a 2-byte instruction: OUT (10H), A. Byte 1: OUT → This is the opcode to output data. Byte 2: (10H*) , A → This is the operand to specify that the byte should be sent from the accumulator to port 10 H . (A hexadecim...