In 8051 Microcontroller there are 24 different instructions under the Arithmetic Group. In total there are 64 opcodes. The Carry Flag (CY), Auxiliary Carry (AC)and Overflow flag (OV) are affected based on the result of ADD, ADDC, SUBB  etc. instructions. The multiple and divide instructions clear the Carry flag, and also does not affect the AC flag. After execution of multiplication, the OV flag will be 1 when the result is greater than FFH. Otherwise, it is 0. Similarly, after division OV flag is 1 when the content of B is 00H before division, otherwise it is 0. The DA ... Read More

In 8051 Microcontroller there is 28 different instructions under the Data Transfer Group. In total there are 79 opcodes. The flags are not affected by using the data transfer instructions, but the P (Parity) flag may change if the value of A register is changed using Data Transfer Instruction. Similarly, when a data is transferred to the PSW register, the flags will change.In the following table, we will see the Mnemonics, Lengths, Execution Time in terms of the machine cycle, Number of Opcodes etc.MnemonicsByte CountExecution TimeOpcode CountMOV A, Rn118MOV A, a8211MOV A, @Ri112MOV A, #d8211MOV Rn, A118MOV Rn, a8228MOV Rn, ... Read More

The instructions of 8051 Microcontroller can be classified into five different groups. These groups are like belowData Transfer GroupArithmetic GroupLogical GroupProgram Branch GroupBit Processing GroupThis Bit-Processing group is also known as Boolean Variable Manipulation.Like 8085, some instruction has two operands. The first operand is the Destination, and the second operator is Source.In the following examples, you will get some notations. The notations are like −Rn = Any register from R0to R7 Ri = Either R0 or R1 d8 = Any 8-bit immediate data (00H to FFH) d16 = 16-bit immediate data a8 = 8-bit address bit = 8-bit address of ... Read More

In this section, we will see different addressing modes of the 8051 microcontrollers. In 8051 there are 1-byte, 2-byte instructions and very few 3-byte instructions are present. The opcodes are 8-bit long. As the opcodes are 8-bit data, there are 256 possibilities. Among 256, 255 opcodes are implemented.The clock frequency is12MHz, so 64 instruction types are executed in just 1 µs, and rest are just 2 µs. The Multiplication and Division operations take 4 µsto to execute.In 8051 There are six types of addressing modes. Immediate AddressingModeRegister AddressingModeDirect AddressingModeRegister IndirectAddressing ModeIndexed AddressingModeImplied AddressingModeImmediate addressing modeIn this Immediate Addressing Mode, the data ... Read More

Now let us see the internal registers, memory and other details from the Programmer’s point of view.There are these componentsEight registers(8-bit) R0 to R7Register A and B.These are also 8-bit registersPSW, Stack Pointer(SP), four ports (P0 to P3). These are also 8-bitDPTR register of 16-bit. This is divided into two 8-bit registers, these are DPH and DPLData RAM from location 08H to 7FHProgram memory from location 0000H to FFFFHProgram Counter (PC) of 16-bit

Internal RAM of the 8051microcontroller has two parts. First one for register banks, bit addressable memory locations, stacks etc. Another part is the SFR(Special function register) area. Only 21 addresses in the SFR area can be used in this microcontroller. Out of these 21 locations, 11are bit-addressable SFR locations.The bit addressable SFRs are like below -RegisterByte addressBit-addressP0 (Port 0)80H80H to 87HP1 (Port 1)90H90H to 97HP2 (Port 2)A0HA0H to A7HP3 (Port 3)B0HB0H to B7HPSWD0HD0H to D7HRegister A (Accumulator)E0HE0H to E7HRegister BF0HF0H to F7HTCON (Timer Control)88H88H to 8FHSCON (Serial Control)98H98H to 9FHIE (Interrupt Enable)A8HA8H to AFHIP (Interrupt Priority)B8HB8H to BFHNow let us ... Read More

The internal data memory of 8051 is divided into two groups. These are a set of eight registers and a scratch pad memory. These eight registers are R0 toR7. The address range 00H to 07H is used to access the registers, and the rest are scratch pad memory. 8051 Provides four register bank, but only one register bank can be used at any point in time. To select the register bank, two bits of PSW (Program Status Word) are used.So the following addressing can be used to select register banks.Address RangeRegister Bank00H to 07HRegister Bank 008H to 0FHRegister Bank 110H to ... Read More

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