ADC
Analog interfaces in control systems
A/D 转换器Convert analog signals into digital signals for use by microprocessors;
D/A 转换器output analog signals for use by external control devices;
D/A principle
The main component of the D/A converter is the resistive switch network, which
is usually controlled by each bit of the input binary number. Through the resistive network, a current proportional to the weight of each bit of the binary number is generated at the input of the operational amplifier, and passed through the operational amplifier. Add and convert to analog voltage proportional to binary number
电压型D/AIt can be regarded as a voltage source and needs to be connected to a large load resistance;
电流型D/Ait can be regarded as the most current source and cannot be connected to a large load resistance (commonly used);
D/A Specifications
Resolution: It is a description of the sensitivity of D/A to small input changes;
for a converter with a resolution of n bits, it can distinguish a full-scale 2-n input signal
Accuracy: including absolute accuracy and relative accuracy
The establishment time is also called the stabilization time: it refers to the time required for the analog output to stabilize to the final value after the digital input of the D/A is added with a full-scale change (such as from all "0" to all "1")
Output level:
for voltage-type D/A converters, the output voltage is 0-5V or 0-10V;
for current-type D/A converters, the output current is several milliamperes to several amperes
Commonly used D/A chip: DAC0832
- An 8-bit D/A chip
- Can be in three different working modes: straight-through mode, single buffer mode, double buffer mode
Another common high-performance chip: DAC1210
A/D principle
The most commonly used A/D converter: successive approximation A/D converter
The composition of successive approximation A/D: successive approximation register (SAR), D/A converter, comparator, timing and control logic and other parts
Conversion principle: successively convert the digital quantity in the set SAR through D/A conversion to obtain the voltage VC, and compare it with the analog voltage VX to be converted
Resolution: Take a chestnut: when the full scale of the input voltage is VFS=10 V, the resolution of the 10-bit A/D converter is 10V/1024≈0.01V
Bus overview
bus concept
Microcomputer generally has the following three buses
- Internal bus: It is the bus between the external chips and the processor inside the microcomputer
- System bus: It is the bus between each plug-in board and the system board in the microcomputer
- External bus: is the bus between the microcomputer and external devices
single bus structure
- When the I/O device exchanges information with the main memory, it does not affect the work of the CPU in principle
- Because there is only one set of buses, when all components are occupied at a certain time, there will be a phenomenon of competing for the right to use the bus
dual bus structure
- It is a structure that separates the memory bus from the I/O bus
multi-bus architecture
- The DMA controller can form a three-bus structure.
The main memory bus is used for information transmission between the CPU and the main memory. The
I/O bus is used for the information transmission between the CPU and various I/O devices.
The DMA bus is used for high-speed peripherals (such as disk, etc.) to exchange information directly with main memory - The four-bus structure realizes the processor link Cache
bus index
Bus width: refers to the number of bits of binary data that can be transmitted at the same time
Data transmission rate: also known as bus bandwidth, refers to the total amount of data that can be transmitted on the bus per unit time
Bus frequency: the bus usually has a basic clock, other on the bus The signals are all based on this clock.
Bus multiplexing Usually, the address bus and the data bus are physically separated.
There are four phases of bus transmission: bus request and arbitration, addressing, data transmission, end
There are two modes of bus transmission: synchronous and asynchronous
PCI bus
PCI bus link diagram
man-machine interface
keyboard interface
There are two main types of keyboards currently used in microcomputers:
- 83-key standard keyboard for PC/XT machines and 84-key keyboard for AT machines
- Enhanced 10l/103/104/105/108/109-key extended keyboard
The keyboard is connected to the host computer through a cable, and every time the keyboard is pressed or released, the corresponding scan code will be sent out. The
start bit of PC/XT scan code transmission format is high level; while the start bit of PC/AT is low level;
Three interfaces corresponding to PC keyboard
mouse interface
There are three types of mice: mechanical mouse, photoelectric mouse and photoelectric mechanical mouse.
- The mechanical mouse drives the gear to generate a signal through the trackball movement
- The photoelectric mouse detects the signal through the infrared light transceiver device
Display interface
video display standard
- MDA Standard: Monochrome Character Display Interface
- CGA Standard: Color Display Adapter
- EGA Standard: Enhanced Graphics Adapter
- VGA standard: array color display interface, 256 colors
- SVGA standard: Super VGA, greatly improved resolution
- TVGA standard: a full-featured video graphics array display interface, which is compatible with all VGA display standards, and extends several new standards for character display and graphic display
CRT monitor
- old-fashioned television and computer monitors, which use cathode ray tube technology to produce images
- By controlling the position and intensity of the electron gun, images of various colors and shapes can be generated on the fluorescent screen
- CRT can achieve high refresh rate and high-quality saturation, but it is prone to screen burn-in and is too bulky
LCD display
- Only active matrix LCD can be in the range of 30 ~ 50ms, passive matrix LCD can not meet the requirements of real-time video
- LCD is backlit
- Due to the backlight characteristics, its display viewing angle is much smaller than that of a CRT display