AT89C51微控制器空分交换系统详细说明书

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"该文档是关于AT89C51微控制器的空分交换系统学习资料，基础的原件说明书，涵盖了芯片的引脚定义、功能特性及描述。" AT89C51是一款基于MCS-51产品系列的低功耗、高性能CMOS 8位微计算机，内置4KB的在系统可编程和可擦除的Flash内存。这种内存具有1000次写入/擦除循环的耐久性，适合于存储程序代码。芯片运行频率范围为0Hz到24MHz，能够在完全静态操作下工作，确保了在各种频率下的稳定性能。该芯片包含128字节的8位内部RAM，提供了足够的空间进行数据处理和临时存储。同时，它有32条可编程的输入/输出线路，这些线路的灵活性使得AT89C51能够适应各种应用需求。此外，它还包括两个16位定时器/计数器，这些计数器可以用于定时、脉冲测量和波特率生成等任务。 AT89C51有六个中断源，增强了系统对实时事件响应的能力。其中，RXD（P3.0）和TXD（P3.1）引脚用于串行通信，INT0和INT1（P3.2和P3.3）用于外部中断，T0和T1（P3.4和P3.5）则与定时器相关。P1.5、P1.6、P1.7、RST引脚分别用于P1口的其他功能，复位信号，以及未指定用途的引脚。此外，还有专门的地址线如A0到A15，数据线如D0到D7，以及WR（P3.6）、RD（P3.7）用于读写控制，XTAL1和XTAL2为晶体振荡器接口，VCC和GND为电源和地线。微控制器还配备了一个可编程的串行通道，支持UART（通用异步接收发送器）通信，这对于实现与其它设备的串行连接非常有用。同时，它还提供了低功耗的空闲模式和电源下降模式，以适应节能需求的应用场景。在硬件编程方面，该芯片具有三级程序存储器锁功能，可以防止未经授权的访问和修改。ALE/PROG引脚用于地址锁存和编程操作，PSEN（程序存储使能）引脚则在读取程序存储器时起作用。总结来说，AT89C51是一款功能丰富的8位微控制器，适用于各种嵌入式系统，尤其是那些需要串行通信、定时功能、中断处理以及低功耗操作的场合。对于空分交换的学习者来说，了解并掌握这款芯片的特性和应用是至关重要的基础。

AT89C51

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 dur-

ing 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 pro-

gram memory.

When the AT89C51 is executing code from external pro-

gram memory, PSEN

is activated twice each machine

cycle, except that two PSEN

activations are skipped during

each access to external data memory.

/VPP

External Access Enable. EA must be strapped to GND in

order to enable the device to fetch code from external pro-

gram memory locations starting at 0000H up to FFFFH.

Note, however, that if lock bit 1 is programmed, EA

will be

internally latched on reset.

should be strapped to V

for internal program

executions.

This pin also receives the 12-volt programming enable volt-

age (V

) during Flash programming, for parts that require

12-volt V

XTAL1

Input to the inverting oscillator amplifier and input to the

internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier.

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, as shown in Figure 1. 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 as shown in Figure 2.

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-flop, but minimum and maxi-

mum 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 spe-

cial 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 execu-

tion, 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.

Figure 1. Oscillator Connections

Note: C1, C2 = 30 pF ± 10 pF for Crystals

= 40 pF ± 10 pF for Ceramic Resonators

XTAL2

GND

XTAL1

Status of External Pins During Idle and Power-down Modes

Mode Program Memory ALE PSEN PORT0 PORT1 PORT2 PORT3

Idle Internal 1 1 Data Data Data Data

Idle External 1 1 Float Data Address Data

Power-down Internal 0 0 Data Data Data Data

Power-down External 0 0 Float Data Data Data

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