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There are many serial interfaces in the process of learning embedded development, such as UART、SPI、I2C etc. ; But parallel interfaces are not common , I'm learning OLED and LCD It is exposed to 8080、8060 Parallel interface machine protocol , So it is necessary to write a blog to explain .

This blog post , Some other blog posts are cited , Links to resources are given later . Here we focus on 8080 The origin of the interface 、 Interface mode and protocol 、 Common interface chips .

Parallel interface

Please Baidu Encyclopedia as a reference

There are also relevant descriptions in microcomputer principle for reference

In a microcomputer system , For example, most of the data transmission between system components use parallel data transmission . Each bit of parallel data corresponds to an independent transmission line , So the data transfer speed block , But there are many lines , Generally, it is only used for short distance transmission . Therefore, in embedded development, the external interface of the chip is mostly serial interface , However, due to the high refresh rate required in the display , therefore OLED and LCD It will still be used in the display 8080 or 8060 Parallel interface for communication .

For the interface chip as the input and output mode of control data 、 I / O data cache 、 Status of data transfer .

8080 and 8060 Interface , In fact, it is not dedicated to LCD The interface of , It was developed from the early processor , be used for CPU Fast transmission with external data (CPU Outspread RAM、ROM), Later it was also used for LCD And printer data transmission .

8080 Parallel interface

1、8080 origin

1974 year , Intel launched In the second paragraph 8 Bit processor Intel 8080, It is Intel 8008 The successor product of , however 8080 It also adds some... To its instruction set 16 Bit operation , have access to 16 Bit address bus , Make it possible to access 64KB Of memory , Its instruction set is better than 8008 Enhanced a lot .

Wikipedia ：https://en.wikipedia.org/wiki/Intel_8080

because 8080 The success of the , For later processor compatibility / Expanding storage lays the foundation , It also affects 32/64 Bit X86 Architecture processor .

2、8080 Interface line

although 8080 Microprocessors have been phased out by the times , But because of 8080 Parallel bus protocol , The advantages in expansion and data transmission are preserved . Many people pursue high speed , The close interface and transmission mode still make 8080 Bus , such as CPU Extend external RAM and ROM,LCD、 Printers are widely used .

CS： Piece of optional signal ——（ If there are multiple decoders available , Access by address ）
WR： Write data control signal ——（ Connect CPU Of RD or IOR）
RD： Read data control signal ——（ Connect CPU Of WR or IOW）
D[7：0]：8 Bit bidirectional data line ——（ Connect CPU data bus ）
RST(RES)： Reset line ——（ Connect the system bus RESET）
D/I（DC）： command / Data signs （0, Read and write commands ;1, Read and write data ）

Here, the timing operation of interface line transmission is described through the interface chip .

3、 Interface chip （ Emphasis on the SSD1306）

3.1、8255A Interface chip

Intel8255A It is a general programmable parallel interface I/O Interface chip , Also known as “ Programmable peripheral interface chip ”, But with CPU Connect to peripherals , have 3 Independent 8 Bit parallel input / Output port .

About 8255A For the detailed introduction of the chip, you can go to the relevant chapters of the microcomputer principle or directly refer to its manual .

3.2、ST 7920 Interface chip

ST 7920 It's classic LCD12864 LCD control chip ,5V drive , With backlight , built-in 128 Characters （8x16） The dot matrix shows RAM（GDRAM）, external CPU Parallel or serial control modes can be adopted . Here is a brief description of parallel control .

3.3、SSD1306 Interface chip

SSD1306 The interface chip is OLED（0.96 " ） The control chip of the display screen , A contrast controller is embedded in the chip 、 Show RAM（GRAM） And crystal oscillator , Therefore, external devices and power consumption are reduced , Yes 256 Level 1 brightness control , Three interfaces can be selected ：6800/8080 In parallel ,I2C and SPI Connect to serial port , Here only for 8080 Parallel introduction .

Structure diagram

The process of reading and writing

First write... According to the need / The type of data read , Set up DC（D/I） For the high （ data ）/ low （ command ）;
Pull down the selection , Choose SSD1306, And then we read the data , Or write the data set RD/WR For low ;
stay RD The rising edge of , Latch data to data line （D[7：0]） On ;
stay WR The rising edge of , Write data to SSD1306 Inside ;

stay 8080 When reading data under mode , We sometimes （ For example, when reading video memory ） Need a fake reading life （Dummy Read）, So that the operating frequency of the microcontroller matches that of the video memory . Before reading real data front , By the process of a false reading . The fake reading here , In fact, the first read byte is discarded. Do not , From the second , That's the data we really need to read .

There are other interface chips , such as ILI9341, There is no introduction here , If you are interested, you can refer to the relevant manuals .

6800 Parallel interface

1、6800 origin

6800（“ 6、 ... and Eight hundred ”） yes Motorola On 1974 Designed and first manufactured in 8 position Microprocessor .MC6800 The microprocessor is M6800 Part of a microcomputer system , The system also includes serial and parallel interfaces IC、RAM、ROM And other supporting chips . An important design feature is , When most other microprocessors require three voltages ,M6800 series IC Just one 5 v Power Supply .M6800 Microcomputer system in 1974 year 3 Published in , It was fully put into operation at the end of that year .

Wikipedia ：https://en.wikipedia.org/wiki/Motorola_6800

because 8080 and 6800 It is a product of the same period , So the interface difference is not very big , There is only a slight difference between the interface lines .

2、6800 Interface line

RES、DB0~7、D/I、CS Signal line and 8080 Are all the same ,6800 take WR、RD Pin becomes ,E： Allow signal （ When multiple pieces are combined , There can be multiple allowable signal lines ）,R/W Read write control （1: read ,0: Write ）

3、 Interface chip

Some of the above interface chips also support 6800 The interface way , Such as SSD1603 Interface chip , I won't give you too much introduction here , Please refer to its manual for details .

8080 and 6800 Interface differences

8080 It's through “ Reading enable （RE）” and “ Write enable （WE）” Two control lines for reading and writing ;
6800 It's through “ Always enable （E)” and “ Reading and writing choices （W/R）” Two control lines for reading and writing .

These are the most obvious differences , Of course, there are some small differences and other details that will be clear when configuring .