Now, in this section we will see how we can use the Zilog Z-80 Microprocessor to add Multi-byte numbers.In this example, we are using 4-byte numbers (56 2F 7A 89)16 and (21 FB A9 AF)16In the memory, at first, we are storing the byte counts, and then the numbers (from least significant bytes to Most significant bytes) in different segments. So after storing the data, the memory structure will be look like thisAddressValue5000H04H...5050H89H5051H7AH5052H2FH5053H56H...5070HAFH5071HA9H5072HFBH5073H21H...Now, we are writing a program at location 8000H to add these two 4-byte number and store the result at location 5090H onwards.ProgramAddressHex CodesLabelsMnemonicsComments800037SCFSet the carry flag80013FCCFComplement the ... Read More

As we know that the Intel 8085 has five interrupt pins (TRAP, RST7.5, RST6.5, RST6.5 and INTR), but the Zilog Z-80 has only two interrupt pin. The NMI and INT . But it has superior interrupt structure compared to 8085.The INT InterruptIt is an active low, level triggered input interrupt. This is maskable and using DI instruction this can be disabled. When the interrupt pin is disabled, the Z-80 will not be interrupted if the IO devices enables the INT pin. Even after the reset, it will be disabled. So if we want that the MPU will be interrupted by the pin, there must be ... Read More

The Zilog Z-80 is 40 pin DIP Microprocessor. Here we will see the actual pin level diagram of Z-80 and also the functional pin diagram of it.This is the actual pin diagram of Z-80 Microprocessor. Now we will see the functional pin diagram of it.Now let us see the Pin functions of the Z-80 microprocessor.PinsTypeFunctionA15 – A0Output16-bit address bus, which provides the addresses for memory (up to 64KB)D7 – D0Input/Output8-bit bi-directional data bus to transfer data between memory/IO devices and CPU.BUSACKOutputIt is Bus Acknowledge pin. It indicates the requesting device that the address bus, data bus, control bus enter into ... Read More

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