中原工学院信息商务学院外文翻译
·Fully static operation: 0 Hz to 24 MHz ·Three-level program memory lock ·128×8-bit internal RAM ·32 programmable I/O lines ·Two 16-bit Timer/Counters ·Six interrupt source ·Programmable serial channel
·Low-power idle and Power-down modes Function Characteristic Description:
The AT89C51 provides the following standard features: 4K bytes of Flash memory, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator and clock circuitry. In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The
Power-down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset. Pin Description:
·VCC: Supply voltage ·GND: Ground
·Port 0: Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs.
Port 0 may also be configured to be the multiplexed low order address/bus during
accesses to external program and data memory. In this mode P0 has internal pull ups.
Port 0 also receives the code bytes during Flash programming, and outputs the code
bytes during program verification. External pull ups are required during program verification.
·Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the internal pull ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull ups.
Port 1 also receives the low-order address bytes during Flash programming and
verification.
·Port 2: Port 2 is an 8-bit bi-directional I/O port with internal pull ups. The Port 2 output
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中原工学院信息商务学院外文翻译
buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull ups.
Port 2 emits the high-order address byte during fetches from external program memory
and during accesses to external data memory which uses 16-bit addresses (MOVX @ DPTR). In this application, it uses strong internal pull ups when emitting 1s. During accesses to external data memory which uses 8-bit addresses (MOVX @ RI). Port 2 emits the contents of the P2 Special Function Register.
Port 2 also receives the high-order address bits and some control signals during Flash
programming and verification.
·Port 3: Port 3 is an 8-bit bi-directional I/O port with internal pull ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pull ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull ups.
Port 3 also receives some control signals for Flash programming and verification. ·RST: Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.
·ALE/PROG: Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory.
If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.
PSEN：·Program Store Enable is the read strobe to external program memory. When the
AT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.
·EA/VPP：External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA
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中原工学院信息商务学院外文翻译
should be strapped to VCC for internal program executions.
This pin also receives the 12-volt programming enable voltage (VPP) during Flash
programming, for parts that require 12-volt VPP.
·XTAL1：Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
·XTAL2：Output from the inverting oscillator amplifier.
·Ready/BUSY: The progress of byte programming can also be monitored by the RDY/BSYoutput signal. P3.4 is pulled low after ALE goes high during programming to indicate BUSY. P3.4 is pulled high again when programming is done to indicate READY. Oscillator Characteristics：
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier
which can be configured for use as an on-chip oscillator. Either a quartz crystal or ceramic resonator may be used.
To drive the device from an external clock source, XTAL2 should be left unconnected
while XTAL1 is driven.
There are no requirements on the duty cycle of the external clock signal, since the input
to the internal clocking circuitry is through a divide by two flip trigger, but minimum and maximum voltage high and low time specifications must be observed. Idle Mode：
In idle mode, the CPU puts itself to sleep while all the on-chip peripherals remain
active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset.
It should be noted that when idle is terminated by a hardware reset, the device normally
resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory. Power-down Mode:
In the power-down mode, the oscillator is stopped, and the instruction that invokes
power-down is the last instruction executed. The on-chip RAM and special function registers retain their values until the power-down mode is terminated. The only exit from power-down is
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中原工学院信息商务学院外文翻译
a hardware reset. Reset redefines the special function registers but does not change the on-chip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. Program Memory Lock Bits:
When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched
during reset. If the device is powered up without a reset, the latch initializes to a random value, and holds that value until reset is activated. It is necessary that the latched value of EA be in agreement with the current logic level at that pin in order for the device to function properly. Programming the Flash:
The AT89C51 is normally shipped with the on-chip Flash memory array in the erased
state (that is, contents = FFH) and ready to be programmed. The programming interface accepts either a high-voltage (12-volt) or a low-voltage (VCC) program enable signal. The low-voltage programming mode provides a convenient way to program the AT89C51 inside the user’s system, while the high-voltage programming mode is compatible with conventional third party Flash or EPROM programmers.The AT89C51 is shipped with either the high-voltage or low-voltage programming mode enabled.
The AT89C51 code memory array is programmed byte-by-byte in either programming
mode. To program any nonblank byte in the on-chip Flash memory, the entire memory must be erased using the chip erase mode. Programming Algorithm:
Before programming the AT89C51, the address, data and control signals should be set
up according to the Flash programming mode table .To program the AT89C51, take the following steps:
1. Input the desired memory location on the address lines. 2. Input the appropriate data byte on the data lines. 3. Activate the correct combination of control signals.
4. Raise EA/VPP to 12V for the high-voltage programming mode.
5. Pulse ALE/PROGonce to program a byte in the Flash array or the lock bits. The
byte-write cycle is self-timed and typically takes no more than 1.5ms. Repeat steps 1 through 5, changing the address and data for the entire array or until the end of the object file is reached. Data Polling:
The AT89C51 features Data Polling to indicate the end of a write cycle. During a write
cycle, an attempted read of the last byte written will result in the complement of the written datum on PO.7. Once the write cycle has been completed, true data are valid on all outputs, and
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中原工学院信息商务学院外文翻译
the next cycle may begin. Data polling may begin any time after a write cycle has been initiated.
Program Verify:
If lock bits LB1 and LB2 have not been programmed, the programmed code data can be
read back via the address and data lines for verification. The lock bits cannot be verified directly. Verification of the lock bits is achieved by observing that their features are enabled. Chip Erase:
The entire Flash array is erased electrically by using the proper combination of control
signals and by holding ALE/PROG low for 10 ms. The code array is written with all “1”s. The chip erase operation must be executed before the code memory can be re-programmed. Reading the Signature Bytes:
The signature bytes are read by the same procedure as a normal verification of locations 030H, 031H, and 032H, except that P3.6 and P3.7 must be pulled to a logic low. The values returned are as follows:
(030H) = 1EH indicates manufactured by ATMEL (031H) = 51H indicates AT89C51 single-chip (032H) = FFH indicates 12V programming (032H) = 05H indicates 5V programming Programming Interface:
Every code byte in the Flash array can be written and the entire array can be erased by using the appropriate combination of control signals. The write operation cycle is self timed and once initiated, will automatically time itself to completion. （2）The sensor DS18B20
In the traditional analog signal distance temperature measuring system, need good solve lead error compensation, multi-point measurement error and amplifying circuit switching technologies such as zero drift error problem, can achieve high measuring accuracy. Another general monitoring site of the electromagnetic environment is very bad, all kinds of jamming signal is stronger, the simulated temperature signal interference and vulnerable to produce measurement error and measuring precision [5]. Therefore, in temperature measuring system, the strong anti-jamming capability of the new digital temperature sensor is the most effective to solve these problems, compared with other temperature sensor DSl820 has the following features:
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