The ATMEL Microcontroller AT89C51
The 89C51 is an 8-bit microprocessor originally designed in the 1980's by Intel that has gained great popularity since its introduction. Its standard form includes several standard on-chip peripherals, including timers, counters, and UART's, plus 4kbytes of on-chip program memory and 128 bytes (note: bytes, not Kbytes) of data memory, making single-chip implementations possible. Its hundreds of derivatives, manufactured by several different companies (like Philips) include even more on-chip peripherals, such as analog-digital converters, pulse-width modulators, I2C bus interfaces, etc. Costing only a few dollars per IC, the 8051 is estimated to be used in a large percentage (maybe 1/2?) all embedded system products.
Some features of the 8051 Micrcontroller are.
• 89C51 Central Processing Unit.
• On-chip FLASH Program Memory.
• Speed up to 33 MHz.
• Fully static operation.
• RAM expandable externally up to 64 kbytes.
• 4 interrupt priority levels.
• 6 interrupt sources.
• Four 8-bit I/O ports.
• Full-duplex enhanced UART.
• Framing error detection.
• Automatic address recognition.
• Three 16-bit timers/counters T0, T1 (standard 80C51) and additional T2 (capture and compare) Power control modes.
• In microcontroller 8051 Clock can be stopped and resumed.
• Idle mode.
• The microcontroller 8051 has Power down mode.
• Programmable clock out.
• Second DPTR register.
• Asynchronous port reset.
• Low EMI (inhibit ALE) .
• Wake up from power down by an external interrupt
The Microcontroller 8051 memory architecture includes 128 bytes of data memory that are accessible directly by its instructions. A 32-byte segment of this 128 byte memory block is bit addressable by a subset of the 8051 instructions, namely the bit-instructions.With Microcontroller 8051 External memory of up to 64 Kbytes is accessible by a special "movx" instruction. Up to 4 Kbytes of program instructions can be stored in the internal memory of the 8051, or the 8051 can be configured to use up to 64 Kbytes of external program memory The majority of the 8051's instructions are executed within 12 clock cycles.
OSCILLATOR CHARACTERISTICS:
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier. The pins can be configured for use as on-chip oscillator. To drive the device from an external clock source, XTAL1 should be driven while XTAL2 is left unconnected. There are no requirements on the duty cycle of the external clock signal, because the input to the internal clock circuitry is through a divide-by-two flip-flop. However, minimum and maximum high and low times specified in the data sheet must be observed.
RESET:
A reset is accomplished by holding the RST pin high for at least two machine cycles (24 oscillator periods), while the oscillator is running. To insure a good power-on reset, the RST pin must be high long enough to allow the oscillator time to start up (normally a few milliseconds) plus two machine cycles. At power-on, the voltage on VCC and RST must come up at the same time for a proper start-up. Ports 1, 2, and 3 will asynchronously be driven to their reset condition when a voltage above VIH1 (min.) is applied to RST. The value on the EA pin is latched when RST is de-asserted and has no further effect.
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The 89C51 is an 8-bit microprocessor originally designed in the 1980's by Intel that has gained great popularity since its introduction. Its standard form includes several standard on-chip peripherals, including timers, counters, and UART's, plus 4kbytes of on-chip program memory and 128 bytes (note: bytes, not Kbytes) of data memory, making single-chip implementations possible. Its hundreds of derivatives, manufactured by several different companies (like Philips) include even more on-chip peripherals, such as analog-digital converters, pulse-width modulators, I2C bus interfaces, etc. Costing only a few dollars per IC, the 8051 is estimated to be used in a large percentage (maybe 1/2?) all embedded system products.
Some features of the 8051 Micrcontroller are.
• 89C51 Central Processing Unit.
• On-chip FLASH Program Memory.
• Speed up to 33 MHz.
• Fully static operation.
• RAM expandable externally up to 64 kbytes.
• 4 interrupt priority levels.
• 6 interrupt sources.
• Four 8-bit I/O ports.
• Full-duplex enhanced UART.
• Framing error detection.
• Automatic address recognition.
• Three 16-bit timers/counters T0, T1 (standard 80C51) and additional T2 (capture and compare) Power control modes.
• In microcontroller 8051 Clock can be stopped and resumed.
• Idle mode.
• The microcontroller 8051 has Power down mode.
• Programmable clock out.
• Second DPTR register.
• Asynchronous port reset.
• Low EMI (inhibit ALE) .
• Wake up from power down by an external interrupt
The Microcontroller 8051 memory architecture includes 128 bytes of data memory that are accessible directly by its instructions. A 32-byte segment of this 128 byte memory block is bit addressable by a subset of the 8051 instructions, namely the bit-instructions.With Microcontroller 8051 External memory of up to 64 Kbytes is accessible by a special "movx" instruction. Up to 4 Kbytes of program instructions can be stored in the internal memory of the 8051, or the 8051 can be configured to use up to 64 Kbytes of external program memory The majority of the 8051's instructions are executed within 12 clock cycles.
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier. The pins can be configured for use as on-chip oscillator. To drive the device from an external clock source, XTAL1 should be driven while XTAL2 is left unconnected. There are no requirements on the duty cycle of the external clock signal, because the input to the internal clock circuitry is through a divide-by-two flip-flop. However, minimum and maximum high and low times specified in the data sheet must be observed.
RESET:
A reset is accomplished by holding the RST pin high for at least two machine cycles (24 oscillator periods), while the oscillator is running. To insure a good power-on reset, the RST pin must be high long enough to allow the oscillator time to start up (normally a few milliseconds) plus two machine cycles. At power-on, the voltage on VCC and RST must come up at the same time for a proper start-up. Ports 1, 2, and 3 will asynchronously be driven to their reset condition when a voltage above VIH1 (min.) is applied to RST. The value on the EA pin is latched when RST is de-asserted and has no further effect.
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