发布时间 : 星期五 文章基于nRF905的无线温度测量系统的研究与设计更新完毕开始阅读
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introduction , but four function of passway these self-same. Expand among the system of memory outside having slice, four port these may serve as accurate two-way mouth of I/O in common use. Expand among the system of memory outside having slice, P2 mouth see high 8 address off; P0 mouth is a two-way bus, send the introduction of 8 low addresses and data / export in timesharing
Output grade , P3 of mouth , P1 of P1 , connect with inside have load resistance of drawing , every one of they can drive 4 Model LS TTL load to output. As while inputting the mouth, any TTL or NMOS circuit can drive P1 of 8051 one-chip computers as P3 mouth in a normal way . Because draw resistance on output grade of them have, can open a way collector too or drain-source resistance is it urge to open a way, do not need to have the resistance of drawing outerly . Mouths are all accurate two-way mouths too. When the conduct is input, must write the corresponding port latch with 1 first . As to 80C51 one-chip computer, port can only offer milliampere of output electric currents, is it output mouth go when urging one ordinary basing of transistor to regard as, should contact a resistance among the port and transistor base , in order to the electricity while restraining the high level from exporting P1~P3 Being restored to the throne is the operation of initializing of an one-chip computer. Its main function is to turn PC into 0000H initially , make the one-chip computer begin to hold the conduct procedure from unit 0000H. Except that the ones that enter the system are initialized normally,as because procedure operate it make mistakes or operate there aren't mistake, in order to extricate oneself from a predicament , need to be pressed and restored to the throne the key restarting too. It is an input end which is restored to the throne the signal in 8051 China RST pin. Restore to the throne signal high level effective , should sustain 24 shake cycle (namely 2 machine cycles ) the above its effective times. If 6 of frequency of utilization brilliant to shake, restore to the throne signal duration should exceed 4 delicate to finish restoring to the throne and operating. Produce the logic picture of circuit which is restored to the throne the signal:
Restore to the throne the circuit and include two parts outside in the chip entirely. Outside that circuit produce to restore to the throne signal (RST ) hand over to Schmitt's trigger, restore to the throne circuit sample to output , Schmitt of trigger constantly in each S5P2 , machine of cycle in having one more , then just got and restored to the throne and operated the necessary signal insidly. Restore to the throne resistance of circuit generally, electric capacity parameter suitable for 6 brilliant to shake, can is it restore to the throne signal high level duration greater than 2 machine cycles to guarantee. Being restored to the throne in the circuit is simple, its function is very important. Pieces of one-chip computer system could normal running,should first check it can restore to the throne not succeeding. Checking and can pop one's head and monitor the pin with the oscillograph tentatively, push and is restored to the throne the key, the wave form that observes and has enough range is exported (instantaneous), can also through is it restore to the throne circuit group holding value carry on the experiment to change.
The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM). The
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device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications.
The AT89C51 provides the following standard features: 4K bytes of Flash, 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.
Idle Mode:
In idle mode, the CPU puts itself to sleep while all the onchip 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 hard ware 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 a hardware reset. Reset redefines the SFRs 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
On the chip are three lock bits which can be left unprogrammed (U) or can be programmed (P) to obtain the additional features listed in the table below.
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.
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