如何读单片机的时序图

/itangcle

CPE/EE 421

Microcomputers

WEEK #10

Interpreting the Timing Diagram

如何读懂时序图

The 68000 Read Cycle

2 Timing Diagram of a Simple Flip-F lop

Idealized form of the timing diagram

Actual behavior of a D flip-f lop

Data hold time

Data setup time

Max time for output to

become valid after clock

Alan Clements 3 General form of the timing diagram

An alternative form of the timing diagram

4

The Clock

•A microprocessor requires a clock that provides a stream of timing pulses to control its internal operations

一个微处理器需要时钟,提供一系列的计时脉冲来控制它的内部操作

•A 68000 memory access takes a minimum of eight clock states numbered from clock state S0 to clock state S7

一个6800芯片的储存器最小能过接收8个从S0到S7的时钟脉冲.

6

A memory access begins in clock

state S0 and ends in state S7

Alan Clements Alan Clements 7

The most important parameter

of the clock is the duration of a cycle,

t C YC .

Alan Clements 8

Address Timing

地址时序

•We are interested in when the 68000 generates a new address for use in the current memory access

我们感兴趣的是当6800芯片能够生成一个新的地址供当前的内存访问

•The next slide shows the relationship between the new address and the state of the 68000 ’s clock

下面展示的是新的地址跟6800芯片时钟的关系

1:

S0在

没有

初始

化的

时

候，

地址

总线

总是

包涵

新的地址。

2： S1这个状态说明一个新的地址可以供内存访问

Alan Clements

Address Timing

地址时序

•Let’s look at the sequence of events that govern the timing of the address bus

让我们看看事件发生的顺序,管理时间的地址总线•The “old” address is removed in state S0

旧的地址已经从S0中移除

•The address bus is floated for a short time, and the CPU puts out a new address in state S1

地址要先存在一小段时间后，CPU才能把心的地址状态写入S1中12

Alan Clements

Alan Clements Alan Clements 13

The old address is removed

in clock state S0 and the

address bus floated

Alan Clements

我们感兴趣的是地址生效的那个时间点。这个时间是在S0失效后，t CLA V 秒后。

t C LA V

The designer is interested in the point at

which the address first becomes valid. This

point is t C LA V seconds after the falling edge

of S0.

Address and Address Strobe

地址跟地址选通

•We are interested in the relationship between the time at which the address is valid and the time at which the address strobe, AS*, is asserted

我们感兴趣的事在地址总线能够访问时，地址选通是否有效。

•When AS* is active-low it indicates that the address is valid

当AS*低电平有效时地址才是有效的。

Alan Clements