basic I/O Interface technology —— Microcomputer Chapter 7 Notes

Preface

Tomorrow's exam , Satcom ！

This chapter is mainly about some knowledge points of parallel interface , involves 8255、8253 There are also serial interfaces .

MindMap

Parallel communication and serial communication

signal communication

Refers to computers and peripherals 、 Between computers Information switching .

The basic method

Parallel communication and serial communication .

Parallel communication

Is to put the data to everyone meanwhile stay Multiple parallel transmission lines for transmission .

advantage

Fast transmission speed , Suitable for high data transmission rate 、 Occasions with short transmission distance .

serial communication

Contrary to parallelism , Press Time sequence Transmit on one transmission line in turn .

characteristic

Transmission speed is slow 、 long-range 、 Low cost , Suitable for long distance 、 Medium and low speed communication .

Overview of parallel interfaces

Parallel interface connection CPU And Parallel peripherals , Realize the Parallel communication .

Hardware structure （ A typical ）

1. Latched or buffered data port .
2. And CPU、 Peripheral devices are necessary for data exchange control and state The signal .
3. Port decoding circuit .
4. Control circuit .

8255A

Pin structure diagram

There are three 8 Bit parallel port , 40 One pin .

working principle

Structure and function

Data port

Yes 3 individual 8 position I/O port （A、B、C）,24 root I/O Line and peripheral exchange data or communication ,C The mouth is divided into two 4 Bit mouth .

A、B For oral use 8 Bit data I/O mouth ,C can 8 position , Or two 4 position , It is also often used to cooperate A Mouth and B mouth , As Control signals Output 、 Or as Status signals Input .

Port address

Control word

Mode selection control word

Definition How each port works .

Three ways ：

1. The way 0—— Basic input and output
2. The way 1—— Strobe input and output
3. The way 2—— Bidirectional bus I/O The way

Set reset control word

Yes C Port of Perform any set or reset operation .

port C Commonly used in control or Answer signal , We can reset and set it , Write through the control port By position / Reset Control word .

Status word

Operation mode

Mentioned earlier ,8255A There are three ways of working , In ways 1 And way 2 when ,C Mouth for A mouth /B The contact signal of the port , use IN Instructions can be read C The state of the mouth .

The way 0—— Basic input / output mode

It is suitable for simple without answering signals I/O occasion .

The output is latched , Input no latch .

The way 1—— Gate input / Output mode

Input

Both input and output pass Answer signal Realization , This is a A/B Used as a data port ,C The part of is used for Handshake signal line And Interrupt request line .

Input of data port 、 Output can be latched .

PC3_{5 and PC0}2 for A Mouth and B State and control line of the port ,PC6~7 Used as a IO Line .

STB－ Data strobe input signal , Low level active , Input by peripheral ;

IBF－ Input buffer full signal , High active , from 8255A Output status signal , Indicates that the input latch is full , The outward setting indicates that no more data can be sent .

INTEA: Interrupt Enable, Interrupt enable signal , Set the interrupt to allow or mask the interrupt signal .INTE No external leads , By software C Set at a certain position 0 Or place 1 The operation of . Yes A mouth , The interrupt permissive end is PC4, Yes B mouth , yes PC2. Set up 1 Allow the interrupt , Set up 0 Mask interrupt .

INTRA: 8255 towards CPU Application interruption , Highly effective , request CPU interrupt .
INTR For Gao you 3 Conditions : 1) STB For the high , That is, the data has been entered 8255; 2) IBF For the high , namely 8255 Data received ;3) INTE( Interrupt request permission ) For the high , namely 8255 Allow answering in interrupt mode .
INTRA For the high , notice CPU Can take 8255A The number in your mouth .

Output

PC3、PC6 and PC7 do A The response signal of the port ,PC0、PC1 and PC2 do B The response signal of the port . The rest of the PC4 and PC5 It can be used as input or output line .

OBF－ Output buffer full signal , Output , Low level active . Express CPU Data has been output to the specified port .

ACK－ Peripheral response signal , Low level active , Sent by peripherals to 8255A. Express CPU The data sent to the specified port has been accepted by the peripheral .

INTE－ Interrupt enable signal .

INTR－ Interrupt request signal , High active .

The way 2—— Bidirectional bus mode （ only A mouth ）

At this time PA7~PA0 As a bidirectional data bus ,PC3 _{PC7 Used as a A The communication control signal of the port .PC2}PC0 It can be used as B The answer signal line of the port , Or make I/O Line .

INTRA－ Interrupt request signal , High active .

OBFA－ Output buffer full , Low level active .

ACKA－ Peripheral response signal , Low level active .

IBFA－ Input buffer full signal , High active .

STBA－ Strobe input signal , Low level active .

C Mouth status word

In ways 1 and 2 when ,C The interface generates contact signals with peripherals , Now read C The content of the mouth , Check or test the status of peripherals .

Lai Duan 8255 The compilation of

MOV DX, 1023H           ; set control port address
MOV AL, 1001X000B       ; set function control word
OUT DX, AL
MOV AL, 0               ; line light port PC0, set low
OUT DX, AL

MOV DX, 1021H           ; port B address
MOV AL, 80H             ; pb7
OUT DX, AL              ; open control

A:
MOV DX, 1020H           ; port A address
IN AL, DX               ; get data
CMP AL, 0               ; if PA0~PA7 have one is hight, it impress have abnormal
JZ A                    ; keep monitor

MOV CX, 3               ; set loop times
MOV DX, 1022H           ; port C address

B:
MOV AL, 1
OUT DX, AL              ; alarm lamp light on
CALL DELAY
MOV AL, 0
OUT DX, AL              ; alarm lamp light off
CALL DELAY
LOOP B
JMP A                   ; keep monitor

Programmable timing / Counter 8253

8253 It's a kind of Hardware timing / Counter chip

One 、 External lead level internal structure

3 individual 16 Bit timing / Counter （ passageway ）
24 Pin dual in line
Maximum counting frequency 2.6MHz
TTL Level compatible
Single power supply +5V Power supply

Channel selection

Two 、 Count start mode

branch Program instructions start （ Soft start ） and The external circuit signal starts （ Hardware boot ） Two processes .

Programming structure

Control word

8253 Control word format

working process

1. Set up 8253 How it works
2. Set count initial value to initial value register
3. first CLK The falling edge signal causes the contents of the initial value register to be placed in the count register
4. Every one in the future CLK The signal , Count register minus 1
5. Reduced to 0 when ,OUT The terminal outputs a special waveform signal
   notes ： The above counting process is also subject to GATE Signal control

3、 ... and 、 Operation mode

Control word D1~D3 In fact, that is Choice of working mode , There are the following 6 Ways of working ：

The way 0—— Interrupt count end
The way 1—— Repeatable monostable trigger
The way 2—— Frequency generator
The way 3—— Square wave generator
The way 4—— Software triggered strobe
The way 5—— Hardware triggered strobe

The way 0 Interrupt count end

Software startup , Do not automatically repeat the count . After loading the control word OUT The terminal becomes low , End of count OUT Output high level .

During counting ,GATE The terminal shall remain high .GATE The signal goes low , Then pause counting , until GATE recovery .OUT The end output is about (N+1)TCLK Negative pulse of width . During the counting process, the initial value can be modified at any time to restart the counting .

The way 1 Monostable trigger

Hardware boot , Do not automatically repeat the count . After loading the control word OUT The terminal becomes high . Counting starts OUT The terminal becomes low , The count goes up again after the end .

Gate signals GATE The jump trigger count of the terminal , Repeatable trigger . If next time GATE The rising edge arrives ahead of time , be OUT The end negative pulse broadening is the sum of two counting processes . Writing a new initial value during counting does not affect this count .

The way 2 Frequency generator

soft 、 Hardware boot , Automatic repeat count . After loading the control word OUT The terminal becomes high , Count to the last CLK when OUT Output negative pulse , And repeat this process continuously .

GATE Control signal for counting ：GATE Lower the count and stop , The next one when it gets higher CLK Falling edge , Recount from initial value .
At the end of each counting cycle （ Reduced to 1 when ）,OUT Output a TCLK Negative pulse of width .
The counting process is automatically repeated .
Modifying the initial value in the counting process does not affect the counting process of this round .

The way 3 Square wave generator

soft 、 Hardware boot , Automatic repeat count . After loading the control word OUT The terminal becomes high , then OUT Continuous output symmetrical square wave ： front N/2 or （N+1）/2 individual CLK,OUT For the high , after N/2 or （N-1）/2 individual CLK, OUT For low .

OUT Output square wave , The first half cycle is high , The second half cycle is low .
Modifying the initial value during counting does not affect the counting process of this half cycle .
GATE It can be used as a control signal for counting ：GATE Lower the count and stop , The next one when it gets higher CLK Falling edge , Recount from initial value .

The way 4 Software triggered strobe

Software startup , Do not automatically repeat the count . After loading the control word, the output terminal becomes high , After counting, output a CLK Negative pulse of width .

During counting ,GATE The terminal shall remain high .
Every time the initial value is written , Count a cycle , Then stop counting .
At the end of each counting cycle （ Reduced to 0 when ）,OUT Output a TCLK Negative pulse of width .
Modifying the initial value in the counting process does not affect the counting process of this round .

The way 5 Hardware triggered strobe

Hardware boot , Do not automatically repeat the count .OUT Terminal waveform and mode 4 identical .

When writing the initial value ,GATE The terminal should be kept low .
GATE Every time a positive pulse appears , Count a cycle , Then stop counting .
At the end of each counting cycle （ Reduced to 0 when ）,OUT Output a TCLK Negative pulse of width .
Modifying the initial value in the counting process does not affect the counting process of this round .

Four 、8253 Application

Three parts ： Connect the system 、 Set the way it works 、 Set initial value of count . The last two are programming .

Initialize program flow

CNT0:
MOV DX, 0123H       ; set control port address
MOV AL, 34H         ; set word funtion is 2
OUT DX, AL
MOV DX, 01020H      ; counting channel 0
MOV AX, 20000
OUT DX, AL          ; clock frequency
MOV AL, AH
OUT DX, AL

I don't understand this either , Look around

MOV DX, 3E3H        ; set control port address
MOV AL, 00110110B   ; chanel 0, function 3
OUT DX, AL
MOV DX, 3E0H        ; chanel 0 port address
MOV AX, 20000       ; 2MHz
OUT DX, AL
MOV AL, AH
OUT DX, AL

XOR AL, AL
MOV DX, 3E5H
OUT DX, AL          ; set 0 let cp goto
MOV DX, 3E4H        ; trisate gate

NEXT:
IN AL, DX
AND AL, 01H
JZ NEXT

MOV DX, 3E5H
MOV AL, 2
OUT DX, AL

GOON:
MOV AH, 1
INT 16H
JZ GOON
XOR AL, AL
OUT DX, AL
MOV AH, 4C
INT 21H

The latter

Other , Serial interfaces and parallel asynchrony are not the focus , So stop writing .