The 8051 has 128 bytes of On-Chip RAM. So for accessing that RAM area, the address space is 00H to 7FH. When we need more data memory, we can use external RAM. The address space of external RAM is 0000H to FFFFH.The external and internal data memory can be added to increase the total amount of data memory. When we are trying to access the external data memory, then the read RD or write WR will be the output from 8051. The external data memory address can be either 8-bit or 16-bit wide. Generally, the one 8-bit address is used ... Read More

We have already discussed that the 8051 microcontroller has the internal program memory. In this chip, there is EA  pin. It indicates the External Access. So by using this pin, we can check whether the internal program memory is used or not. So when there is a low signal in this pin, the internal 4K bytes of program memory is not used, but in this situation, it can access only the ROM.When we are trying to access the external data memory, then the read RD or write WR will be the output from 8051. So for reading the data from ... Read More

There are various versions of 8051 Microcontroller. These versions are 8051H, 8051BH and 8051CH. Here we will see the general 8051 Microcontroller. This microcontroller works on a +5V dc power source. As it has on-chip clock circuit, so we need only the crystal oscillator between the pin XTAL1 and XTAL2 with two additional capacitors. As we have mentioned that the general clock frequency is 12MHz, but some other version of 8051 uses 20MHz crystal oscillator. There is a clock dividing circuit to divide the clock frequency to provide an internal clock pulse. So for 12MHz clock, it is divided into ... Read More

We have seen some of the features of 8051 microcontrollers. Now in this section, we will discuss different features of it. The 8051 Features are like below8051 has 8-bit Processing Unit to control applications.Using 8051 we can process bits, or in other words, the bit processing capability is present in the 8051microcontroller.8051 has separate Data memory and separate program memory spaces. The program memory is basically 4KBof on-chip EPROM (address space 0000H to 0FFFH), and 128 bytes of RAM (address space 00H to 7FH)There is total 64KB of program memory address space including the on-chip 4KB space.The RAM Address space (128 ... Read More

The 8051 Microcontroller is designed by Intel in 1981. 8051 is 40 pin DIP IC. This is an 8-bit microcontroller.It is a very famous Microcontroller of Intel family. As we know Microprocessor like 8085, Z-80 or M6800 contains the ALU, control unit and some registers, but there were no internal storages. The Microcontroller contains the RAM and ROM, IO ports inside it. Some microcontroller also contains the ADC in it. As most of the required components are inside the chip, so the cost of application is also reduced.These kinds of microcontrollers are used in different appliances like televisions, washing machines, ... Read More

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 ... Read More

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 More

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 More

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 More

In this section, we will see the basic architecture of the Motorola M6800 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. So from this diagram, we can see that there are two 8-bit Accumulators A and B, some 16-bit registers (Program Counter PC, Index Register IX, Stack Pointer SP), and 8-bit flag register CCR.Both of the Accumulators Aand B have the same prominence in the Instruction set. There are very few instructions in 6800, where the Accumulator A is used but B ... Read More