Parallel interface 8255A

1 8255A function

1. Three 8 Bit parallel input / Output port , It can be determined programmatically
2. Can adapt CPU And I/O Requirements for multiple data transmission modes between interfaces

2 8255A Internal structure and pin diagram

8255A Yes 3 Ports ,40 One pin ,3 Ways of working

This is from the teacher's courseware

Personally, I think the reference books are better

1） Data bus buffer
It's a two-way three state 8 Bit buffer , And CPU The system is connected to the data bus , yes 8255A And CPU The only way to transfer data between . input data 、 Output data 、 The control command words are transmitted through the data bus buffer .
2） Read write control logic
read / The write control logic receives data from CPU Address bus signals and control signals , And issue commands to two control groups (A Group and B Group ). It controls CPU Send the control command or output data to the corresponding port ; Or send the status of the peripheral or the input data from the corresponding port to CPU.
3）A Group and B Group control
A,B and C The way the three ports work is CPU By writing... To the control register A Group and B Group mode control word . port A And port C The height of 4 position (PC~7~-PC~4~.) constitute A Group , from A The group control unit controls it ; port B And port C It's low 4 position (PC~3~-PC~0~) constitute B Group , from B The group control unit controls it .

1. port A：PA0～PA7
   A Group , Support working methods 0、1、2
2. port B：PB0～PB7
   B Group , Support working methods 0、1
3. port C：PC0～PC7
   Only working mode is supported 0
   A Group control high 4 position PC4～PC7
   B Group control low 4 position PC0～PC3

3 8255A Control word

There are two control words , And write... To the same control port .

1. Mode control word

2. Set up / Reset control word
   

4 8255A Operation mode

1. The way 0： Basic input / Output mode
   （1） Two 8 Bit port (A、B) And two 4 Bit port (C On 、 Next ) Can work in this way ;
   （2） Any port can input / Output ;
   （3） Output data latch , Input data does not latch ;
   （4） The input of each port / The output can have 16 Combinations of .
   It is suitable for unconditional transmission and query mode interface circuit .

2. The way 1： Gate input / Output mode
   （1） The way 1 Next , There are two sets of ports , Each group contains one 8 The number of digits depends on the mouth and 3 Control lines ;
   （2） Each group of ports provides interrupt request logic and interrupt allow trigger ;
   （3） Two sets of ports can work in the same mode 1;
   （4） Input / All output data are locked .
   Interface circuit for query and interrupt mode .
   

3. The way 2： Two way gated transmission mode
   （1） This method can only be used for A Group ;
   （2） In this way, there is a 8 Bit bidirectional data port and 5 A control line ;
   （3） Input / All output data are locked .
   Peripherals for two-way transmission of data .
   

5 8255A Interface with printer （ The way 0）

working process ：

1. The host sends the data to the pin DATA~0~～~7~;
2. At the same time, the data strobe signal is sent STROBE ;
3. The printer is BUSY A busy signal is sent on the signal line ;
4. The printer cancels the busy signal after processing the data .

6 LED Nixie tube

1. form
   The main part is 7 Segment light emitting tube , Clockwise is called a、b、c、d、e、f、g, Some products also come with a decimal point h.
2. function
   Can display 0～9, A～F, And some special characters , Such as －、P etc. .
3. Two structures