An Embedded PC Non-standard Keyboard Circuit Design

7050 OSC seed vibration

One-piece inductor

With the rapid development of embedded systems, embedded PCs have been widely used. The standard PC keyboard cannot meet the requirements in most cases due to its large size and many buttons. Based on the introduction of PS/2 communication protocol, this paper uses AT89C52 to realize the design of a PC non-standard keyboard. The complete hardware implementation circuit diagram and the main software development methods are given. The keyboard has the characteristics of simple structure, stable operation, and easy expansion, and has been specifically applied in a certain type of aerial image return transmission system.

Figure 1 is a schematic diagram of the keyboard circuit, which is composed of ATMEL's microcontroller AT89C52, logic system and matrix keyboard. The AT89C52 MCU mainly completes the keyboard scan, determines the information that the keyboard is closed and disconnects, and sends the key code and synchronous clock to the industrial computer; the logic system provides the start-up signal and the watchdog timing reset function to prevent the crash; the matrix keyboard is 4&TImes; The determinant keyboard generates a low-level trigger signal when a key is pressed, which is convenient for the single-chip microcomputer to detect an effective key operation. The keyboard is composed of 4 & TImes; 4 = 16 buttons, wherein the row line is P0.4 ~ P0.7, and the column line is P0.3 ~ P0.0. P3.0 is the key code data output, P3.1 is the synchronous clock, which is output to the PS/2 port of the embedded PC respectively; the +5V power supply is provided by the host. Since the IO port of the AT89C52 is 32, in addition to the input and output terminals CS, SI, SO, SCK of the watchdog circuit, and the key data output terminal Data and the clock output terminal Clock, 26 available ports remain, so that The maximum independent response 13&TImes; 13=169 key inputs, not only can meet the multi-key requirements of the standard keyboard, but also meet the requirements of the common control keys of the industrial computer. The X25045 is a watchdog circuit that receives the CS signal from the AT89C52 in real time and automatically determines the interval between the two signals. When the time interval reaches the set time, its RST output remains low; otherwise, its RST output outputs a high level, and the AT89C52 is reset. In addition, an LED is added to indicate the working state of the keyboard.

Figure 1 keyboard circuit schematic

The AT89C52 microcontroller has the following features: (1) programmable flash memory with 8K bytes; (2) 256 & TImes; 8 bytes of internal RAM; (3) 32 programmable I/O lines; (4) 3 16-bit timing Counter; (5) 8 interrupt sources; (6) Programmable serial UART channel.