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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
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
DefinitionBit stuffing is the mechanism of inserting one or more non-information bits into a message to be transmitted, to break up the message sequence, for synchronization purpose.Purpose of Bit StuffingIn Data Link layer, the stream of bits from the physical layer is divided into data frames. The data frames can be of fixed length or variable length. In variable - length framing, the size of each frame to be transmitted may be different. So, a pattern of bits is used as a delimiter to mark the end of one frame and the beginning of the next frame. However, if the ... Read More
The differences between byte stuffing and bit stuffing can be done under the following heads −What are byte stuffing and bit stuffing?Byte stuffing is a mechanism to convert a message formed of a sequence of bytes that may contain reserved values such as frame delimiter, into another byte sequence that does not contain the reserved values.Bit stuffing is the mechanism of inserting one or more non-information bits into a message to be transmitted, to break up the message sequence, for synchronization purpose.Purposes of byte stuffing and bit stuffingIn Data Link layer, the stream of bits from physical layer are divided ... Read More
Framing is a Data Link layer function whereby the packets from the Network Layer are encapsulated into frames. The data frames can be of fixed length or variable length. In variable - length framing, the size of each frame to be transmitted may be different. So, a pattern of bits is used as a delimiter to mark the end of one frame and the beginning of the next frame.The two types of variable - sized framing are −Character-oriented framingBit - oriented framingCharacter - Oriented FramingIn character - oriented framing, data is transmitted as a sequence of bytes, from an 8-bit ... Read More
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
This is one of the methods of representing signed integers in the computer. In this method, the most significant digit (MSD) takes on extra meaning.If the MSD is a 0, we can evaluate the number just as we would any normal unsigned integer.If the MSD is a 1, this indicates that the number is negative.The other bits indicate the magnitude (absolute value) of the number.If the number is negative, the other bits signify the 2'scomplement of the magnitude of the number.Thus a positive number has the same representation in SM, 1's complement, and 2's complement notations. Only negative numbers are represented ... 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
To represent fractions may be necessary quite often inside the computer. For example, it may be needed to represent inside a computer a value like +0.610 or -0.610. To represent signed fractions, it is necessary to assume the binary point just after the MSB in the bit sequence. Such numbers where the binary point is assumed to be at a fixed position in the bit sequence are called fixed-point numbers.Unsigned fractions will have the assumed binary point at the extreme left. SM, 1's complement, and 2's complement fractions will have this imaginary binary point just to the right of the ... Read More
As an example, the value of 1 001, if the interpretation is that it is a 2's complement fraction will be as follows -It is 1.001 assuming the binary point after the MS bit. As the MS bit is 1, it is a negative number. Then the remaining bits do not specify the magnitude directly. The 2's complement of 1 001 is 0110+ 1 = 0 111. This is a positive fraction with the value 1 × 2−1 +1 × 2−2 +1 × 2−3 = 0.5 + 0.25 + 0.125 = 0.875 decimal. Thus, -0.875 is the value of 1001.If ... Read More