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8085 Articles
Page 5 of 36
IN and OUT instructions in 8085 Microprocessor
In 8085 Instruction set, there are two instructions in 8085 for communication with I/O ports. They are the IN and OUT instructions. The IN or OUT instruction mnemonics should be followed by an 8-bit port address. Thus we can have 28 = 256 input ports and 256 output ports are possible in 8085-based microcomputers. IN and OUT both are 2-Bytes instructions.Mnemonics, OperandOpcode(in HEX)BytesIN Port-addressDB2OUT Port-AddressD32In case of IN instruction, the current 8-bit content of the PORT# will be made available on to the Accumulator. Let us suppose with the PORT#, 8 DIP switches are connected. And their states are ON-ON-OFF-ON-ON-ON-OFF-ON. ...
Read MoreExecution of 'DAD rp' instruction
In 8085 Instruction set, for 16-bit addition, there is one instruction available that is DAD rp instruction. It is a 1-Byte instruction. With this instruction, with the content of the HL register pair, the contents of the mentioned register pair will get added and the result thus produced will be stored on the HL register pair.Mnemonics, OperandOpcode(in HEX)BytesDAD B091DAD D191DAD H291DAD SP391As an example, let us consider the execution of the DADB instruction. Let us suppose, that the initial content of HL register pair is 5050H and content of BC register pair is 4050H. So now if we execute instruction ...
Read MoreHLT instruction in 8085
In 8085 Instruction set, HLT is the mnemonic which stands for ‘Halt the microprocessor’ instruction. It is having a size of 1-Byte instruction. Using these particular instructions, as 8085 enters into the halt state, so we can put the8085 from further processing of next instructions. This is indicated by S1 and S0 control signals. During the halt, S1 and S0 output signals will become 0 0. Mnemonics, OperandOpcode(in HEX)BytesHLT761The 8085 comes out of the Halt state when a valid interrupt occurs. In such a case, it executes the corresponding interrupt service subroutine depending upon the interrupt number and then it continues ...
Read MoreIN a8 instruction in 8085 Microprocessor
In 8085 Instruction set, IN is a mnemonic that stands for INput the Byte from input port’s content to the accumulator. Input port’s 8-bit address is indicated in the instructions as a8. It occupies 2 Bytes in the memory. First Byte specifies the opcode, and the next Byte provides the 8-bit input port address. Mnemonics, OperandOpcode(in HEX)BytesIN Port-addressDB2IN F0H is an example instruction of this type. The result of execution of this instruction is shown below with an example.BeforeAfter(A)Any ValueABHInput Port F0HABHABHIN instruction is the only instruction using which read the input port content to the Accumulator. A possible chip select ...
Read MoreMotorola M6800 Microprocessor
The Motorola M6800 is 40pin DIP IC. It is an 8-bit Microprocessor. It was introduced in 1974 by Motorola. It was designed nearly at the same time when the 8080 was introduced. Like 8080, it also had 16-bit address bus to handle 64KB of data, and 8-bit data bus to read and write data. The M6800 has very few registers. It has two Accumulators A and B, and the Index Register. This Microprocessor only supports the memory mapped IO because there is no instruction regarding IO operations in its instruction set.The M6800 has six addressing modes, 72 instructions and at least ...
Read MorePin description of 6800
The Motorola M6800 is 40pin DIP Microprocessor. Here we will see the actual pin level diagram of M6800 and also the functional pin diagram of it.The M6800 requires some additional chips to provide the required functions. These chips are:6870 (clock generator)6830 (ROM) or 68708(EPROM)6810 (RAM)6820 (PeripheralInterface Adapter)6850 (AsynchronousCommunications Interface Adapter)6828 (PriorityInterrupt Controller)Now see the Pin Level diagram of Motorola M6800This is the actual pin diagram of the M6800 Microprocessor. Now we will see the functional pin diagram of it.Now let us see the Pin functions of the M6800 microprocessor.PinsTypeFunctionA15– A0Output16-bit address bus, which provides the addresses for memory (up to ...
Read MoreAddressing modes of 6800
We have seen the Internal structure and registers of Motorola M6800 Microprocessor. In this section we will see the addressing modes of M6800.There are six addressing modes in M6800 MPU. These modes are −Immediate Addressing ModeImplied Addressing ModeDirect Addressing ModeExtended Addressing ModeIndexed Addressing ModeRelative Addressing ModeNow Let us see some basic syntax of M6800 Assembly Language Programming.If a number is 8CH in hexadecimal, then we have to use $ sign before it. So it will be $8C. A number without $ is treated as decimal number. Similarly, an immediate data is denoted by # symbol. #50FF is a data, but ...
Read MoreInstruction set of 6800
In this section, we will see the different types of instructions of Motorola M6800 microprocessor. There are 72 different types of instructions and 197 different opcodes. So there are 51 1-Byte instruction, 103 2-Byte instruction and 43 3-Byte instruction.As we know that the Intel 8085 has 246 opcodes, though 6800 is more powerful than 8085. The Z-80 has 700 instructions but M6800 has some more advanced branching instructions.The different instruction groups are like these −Data Transfer GroupArithmetic GroupLogical GroupBranch GroupMiscellaneous InstructionsData transfer GroupIn this group, there are 14 instructions. We can find 38 opcodes for these 14 instructions. These instructions ...
Read MoreInterrupts of 6800
In Motorola M6800, there are two hardware interrupt pins. These pins are NMI and. IRQ These pins are active low input pins. The first one is non-maskable and the second one is maskable and lower priority interrupt. When the IM flag is 1, or CCR register is set, the interrupt is masked or disabled.When the Micro processor enters into some Interrupt Service Subroutine (ISS), it uses SEI instruction to mask the interrupt even if the IRQ activated. The reverse action can be performed using the CLI instruction. It can unmask the interrupt.When in the interrupt is occurred, the M6800 follows ...
Read MoreProgramming examples of 6800
Now, in this section, we will see how we can use the Motorola M6800 Microprocessor to add multi-Byte numbers.AddingMulti-Byte NumberIn 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 looking like thisAddressValue5000H04H...5050H89H5051H7AH5052H2FH5053H56H...5070HAFH5071HA9H5072HFBH5073H21H...Now, we are writing a program to add these two 4-Byte number and store the result at location 5090H onwards.Program CLC LDX#$5050 ...
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