Here we will see the addressing modes of the Zilog Z-80 Microprocessor. But at first we will discuss about the mnemonics of Z-80.As we know there are many similarities between Intel 8085 and Zilog Z-80, so we can also find the similarity on the instructions. But in Z-80 the Mnemonics are slightly different. The Hex codes are same, but only the mnemonics are different. So, if we want to execute a program, which was written in the 8085 MPU, it will work fine. But Z-80 has many other instructions, which are not available in the 8085.Here is the list of ... Read More

In this section we will see some advanced features of Zilog Z-80 Microprocessor. These features are basically compared to the Intel 8085 Microprocessor.The features are listed below −Sr.No.Features & Description1Opcode CountIn this Microprocessor there are 698 Opcodes of different lengths.2Instruction LengthThe instructions can be divided into four categories according to their lengths.There are 202 of 1-byte instructions, 344 of 2-byte instruction74 of 3-byte instruction78 of 4-byte instruction3Opcode LengthThe instructions can also be divided into two parts according to the opcode length. In the instruction set, there are instructions with 1-byte opcode and 2-byte opcode.The number of 1-byte opcode instruction is ... Read More

In this section we will see the basic architecture of the Z-80 Microprocessor, and different registers to write programs into it.To write programs we have to care about the registers and some instructions to access them during program execution.From this diagram it is clear that there are some special purpose registers like W, Z, some other registers like Stack Pointer (SP), Program Counter (PC) etc. three general purpose register pairs (BC, DE, HL) and Accumulator A. There is also an 8-bit flag register to hold the flag bits. Up to this, it is like the 8085 architecture, but in Z-80, ... Read More

The Intel 8080 microprocessor was the predecessor of the 8085 or the Z-80 microprocessors. It was designed and manufactured by Intel. This Microprocessor was released on April 1974. It was an 8-bit Microprocessor.The Intel 8085 is also an 8-bit Microprocessor, which was introduced in 1976. It is very close to the 8080 microprocessor, but some slight changes and modifications are present. The Zilog Z-80 was also introduced in 1976. Basically, the Intel team was divided and formed a new Group called Zilog. The Zilog team was introduced the Z-80 Microprocessor.The 8080 MicroprocessorIn this diagram, we can see that the 8080 ... Read More

Problem Statement − Move a block of 16 data stored from 8050H to 805FH to a target location from 8070F to 807FH. Address Hex Codes Label Mnemonic T-States Comment 8000 21 50 80 START: LXI H, 8050H 10 Setup HL pair as a pointer for source memory. 8003 11 70 80 LXI D, 8070H 10 Set up DE pair as a pointer for destination memory 8006 06 10 MVI B, 10H 7 Set up B to count 16 bytes 8008 7E LOOP: MOV A, M 7 Get ... Read More

In 8085 Instruction set, NOP is an instruction which is falling under Machine Control Instruction category. NOP is a mnemonic that stands for “No Operation”. This instruction does nothing during execution. Only it occupied 1-Byte of memory space and spends 4-Machine Cycles. Mnemonics, Operand Opcode(in HEX) Bytes NOP 00 1 In spite of the fact that it does nothing, still it has got many different applications. It is useful in the following cases − NOP instruction can be used to create small-time delay in the execution of the code. It is very ... Read More

In 8085 Instruction set, DAD SP instruction is a special case of DAD rp instruction. In this instruction contents of HL and SP will get added and sum thus produced will get stored onto HL register pair. It occupies only 1-Byte in memory. Mnemonics, Operand Opcode(in HEX) Bytes DAD SP 39 1 Let us discuss about this instruction execution with one example. We are considering that HL and SP registers are having initial contents as 4050H and 5050H. So after execution of DAD SP instruction, the addition result will be 90A0H which will get ... Read More

In 8085 Instruction set, DCX SP instruction is used to decrement the SP contents by 1. DCX SP instruction is a special case of DCXrpinstruction which decreases the content of the register pair. This instruction occupies only 1-Byte in memory. Mnemonics, Operand Opcode(in HEX) Bytes DCX SP 3B 1 Let us consider that the initial content of SP is 4050H. So after decrement of the content of SP by using DCX SP instruction, SP would have the value 404FH. Here is the required tracing table as below − Before After ... Read More

In 8085 Instruction set, INX SP instruction is used to increment the SP contents by 1. INX SP instruction is a special case of INX rp instruction which increases the content of the register pair. This instruction occupies only 1-Byte in memory. Mnemonics, Operand Opcode(in HEX) Bytes INX SP 33 1 Let us consider that the initial content of SP is 4050H. So after increment of the content of SP by using INX SP instruction, SP would have the value 4051H. Here is the required tracing table as below − Before ... Read More

In 8085 Instruction set, XTHL is a mnemonic that stands for “eXchange Top of stack with HL”. This instruction exchanges the contents of the top two locations of the stack with the contents of register pair HL. Here it is not an exchange between SP with HL.It occupies only 1-Byte in memory. Mnemonics, Operand Opcode(in HEX) Bytes XTHL E3 1 The result of execution of this instruction XTHL is shown below with a sample instruction and along with tracing table. Let us consider HL and SP are having contents BBAAH and 4050H. And ... Read More