This Pin also gives program pulse input during programming of EPROM. If we use multiple memory chips then this pin is used to distinguish between them.It is activated periodically with a constant rate of 1/6th of oscillator frequency. This Pin is used for ALE that is Address Latch Enable. If we use an external ROM then it should have a logic 0 which indicates Micro controller to read data from memory. In order to use the external memory it is required to provide the low voltage (0) on both PSEN and EA pins. PIN 30 is called ALE (address latch enable), which is used when multiple memory chips are connected to the controller and only one of them needs to be selected.We will deal with this in depth in the later chapters. If external memory is connected then PIN 31, also called EA/VPP, should be connected to ground to indicate the presence of external memory. In order to program this we need to supply a voltage of +12V at pin 31. The 8051 chip needs +5V 500mA to function properly, although there are lower powered versions like the Atmel 2051 which is a scaled down version of the 8051 which runs on +3V.Īs described in the features of the 8051, this chip contains a built-in flash memory. Pins 40 and 20 are VCC and ground respectively. The 8051 has a built-in oscillator amplifier hence we need to only connect a crystal at these pins to provide clock pulses to the circuit. (Pin should be held high for 2 machine cycles.) PIN 9 is the reset pin which is used to reset the microcontroller’s internal registers and ports upon starting up. By some estimations, 8051 family chips make up over 50% of the embedded chip market. Typical applications Ĩ051 chips are used in a wide variety of control systems, telecom applications, robotics as well as in the automotive industry. Variants of the 8051 may also have a number of special, model-specific features, such as UART, ADC, Op_Amps, etc., making it an even more powerful microcontroller. 1 Microsecond instruction cycle with 12 MHz Crystal.16-bit program counter and data pointer.Four 8-bit ports, (short models have two 8-bit ports).Bit as well as byte addressable RAM area of 16 bytes.16 bit timers (usually 2, but may have more, or less).Some of the features that have made the 8051 popular are: All these things are called 8051 because they can all be programmed using 8051 assembly language, and they all share certain features (although the different models all have their own special features). The Short and Standard chips are often available in DIP (dual in-line package) form, but the Extended 8051 models often have a different form factor, and are not "drop-in compatible". There are 3 basic "sizes" of the 8051: Short, Standard, and Extended. The Intel 8051 is an 8-bit microcontroller which means that most available operations are limited to 8 bits.
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