The 8085 instruction set is classified into the following three groups according to word size: 1. One-word or 1-byte instructions 2. Two-word or 2-byte instructions 3. Three-word or 3-byte instructions
There are 74 instructions in the 8085 microprocessor.
The 8085 instruction set is classified into three groups according to its Word size. They are 1. One word /1 byte instructions 2. Two word / 2 byte instructions 3. Three word / 3 byte instructions
2 nibbles are in one byte
There are three fetch cycles in a three byte instruction. The first one is four clock cycles long, while the other two are three clock cycles long. Depending on what the instruction does, there will then be more read/write cycles.
Depending on the particular microprocessor, a machine cycle is the fetch or store of one (typically, one byte) native word. In the 8085, this is a byte fetch or store, plus the overhead in decoding and processing the instruction. In this case, the first machine cycle is four clock cycles, or T states, and subsequent machine cycles are three clock cycles, although certain instruction sequences, such as DAD, require two extra clock cycles.
two
A two-byte instruction gives the specific function instruction in two bytes, or two words. The first specifies the opcode, which tells the microprocessor what operation will occur. The second specifies the operand, or the data that the operation is done on.
A double byte is two bytes.
If two bits of a byte are in error when the byte is read from ECC memory, ECC can detect the error.
There are two nibbles in a byte.
An instruction is a command to the microprocessor to perform a given task on specified data. Each instruction has two parts: One is task to be performed,called the operation code (opcode). Second is the data to be operated on, called the operand. It can be specified in various ways,it may include 8bit/16bit data, an internal register, a memory location , or 8bit/16bit address. In some instructions, the operand is implicit. The 8085 instruction set is classified into three groups according to Word size. They are- 1. One word / 1 byte instructions 2. Ttwo word / 2byte instructions 3. Three word / 3byte instructions