What are the requirements for receiving SMS alarm through serial port?

A good article introducing basic knowledge, although written earlier, is still good as basic knowledge. ...

Due to the early writing, the introduction may not be comprehensive. Welcome altar friends to supplement and improve.

With the continuous enhancement of PC's extended functions and the increase of connectable peripherals, if nonstandard connection specifications are adopted, it will inevitably lead to information mismatch in speed, timing, data format and type, so various external interface standards have emerged. The external interfaces of standard PC usually include serial port, parallel port, PS/2 interface, USB interface, network interface, audio interface and VGA interface. This will be introduced in this article and subsequent articles respectively, and the motherboard will be introduced to you in this article.

A. parallel port/interface.

The parallel port adopts a 25-pin double-row socket, which can be used to connect scanners, ZIP drives and even external network cards, tape drives and some extended hard disks. Let's take a brief look at the development history of parallel port:

The original parallel port design is one-way data transmission, which means that data can only be input or output at a certain moment. Later, IBM developed a bidirectional parallel port technology, called SPP (standard parallel port), which can input and output data at the same time, thus turning the original semi-interactive parallel port into a real interactive parallel port. Intel, Xircom and Zenith introduced EPP (Enhanced Parallel Port) in 199 1 * *, which allows the transmission of larger data (500 ~ 1000 bytes/s), and is mainly used for non-printer devices that require high data transmission speed, such as storage devices. Following the launch of EPP, in 1992, Microsoft and HP jointly launched a new parallel port standard called ECP (Extended Function Port). Unlike EPP, ECP is a standard specially formulated for printers. IEEE 1284 published in 1994 covers two standards, EPP and ECP, but both the operating system and the hardware need to support this standard, which is no longer a problem for the current hardware. At present, all the parallel ports we use support EPP and ECP, and we can set the working mode of parallel ports ourselves in CMOS.

Second, the serial interface (serial port)

In the early PC system, the serial port has two physical connection modes, 9-pin and 25-pin, which are connected to the computer through an additional daughter card baffle, as shown in the following figure.

With the development of PC technology, 25-pin serial port is gradually eliminated. At present, all serial ports are directly integrated on the motherboard through 9-pin connection. Generally, PC motherboards provide two serial ports.

The standard serial port can reach the highest data transmission speed of 1 15Kbps, while some enhanced serial ports such as ESP (enhanced serial port) and Super ESP (super enhanced serial port) can reach the data transmission speed of 460Kbps.

Although the motherboard generally integrates two serial ports, Windows can provide up to eight serial port resources for hardware setup (serial number COM 1 to COM8). Although their I/O addresses are different, * * only accounts for two IRQ4 (1,3,5,7 * * * enjoys IRQ4,2,4,6,8). We often encounter this problem in use-if you install a serial mouse or other peripherals on COM 1, you can't install other hardware such as Modem on COM3, because IRQ settings conflict and it can't work. At this time, players can install other peripherals on COM2 or 4.

Third, USB (Universal Serial Bus) interface

1. Introduction

USB (Universal Serial Bus) interface is an interface standard jointly proposed by Compaq, IBM, Microsoft and other companies at the end of 1994. Its purpose is to replace the traditional serial port and parallel port, which are gradually unable to meet the needs of peripherals. 1996, the industry officially adopted the USB 1.0 standard, but it was not popular until the USB 1.0 standard was established and the Win98 kernel was officially provided because the mainstream Win95 did not support it at that time (until Win95 OSR2 provided support for USB1.0 through plug-in modules).

The USB interface on the computer is a plane interface with four golden finger pins (as shown above). If we cut the data line of the USB peripheral, we can find that there are four wires inside, two of which are responsible for power supply and the other two are responsible for data transmission, as shown in the figure below.

There are two kinds of connecting wires for USB interface. Usually, we refer to the end connected to the computer interface as the "A" connector, and the connector connected to the peripheral equipment as the "B" connector (usually, the peripheral equipment is a built-in USB data cable and only contains the "A" connector connected to the computer). The "A" connector represents the "upstream" of the computer; The "B" connector means "downstream" of the peripheral. In this way, different structures and definitions are adopted to avoid confusion and trouble in connection.

2. Performance characteristics of 2.USB interface

● Hot plug, easy to use.

The USB interface is truly hot-swappable. When installing hardware, you don't need to go through the complicated process of shutdown-connection-startup-driver installation-restart, and really realize PnP (Plug and Play) in the startup state. Moreover, USB interfaces have their own reserved interrupt numbers (automatically assigned by USB drivers and automatically restored after unplugging USB devices), which will not compete with other devices for limited resources and can avoid many configuration troubles.

● Wide bandwidth and high speed.

The USB 1. 1 protocol allows 1.5Mbps and 12Mbps, which are respectively 10 times of the standard serial port (1/5 kbps) and 10 times of the standard parallel port.

Note:1Mbps = 0.125mb/s.

● There are many devices that can be connected.

In theory, USB interface can be extended to daisy-chain connection 127 devices through USB Hub, and the effective distance between nodes is 5 meters, which can be extended to 30 meters through USB Hub. However, it should be noted that when using the USB Hub expansion interface, only five Hubs are allowed to cascade at most, and there is an effective distance limit of 30 meters.

● Simple network interconnection function

Using USB interface can realize the interconnection between two computers, carry out simple data exchange and form the simplest peer-to-peer network.

It must be pointed out that the realization of USB2.0 function needs the support of both hardware and software, including the USB main control chip and operating system of the motherboard. As far as the mainstream Windows operating system is concerned, only Win2000 and WinXP can provide complete support for USB2.0. Although the system can recognize USB2.0 devices under other Windows operating systems, it can't run in high-speed mode, and non-mainstream operating systems including Linux, MAC OS, BEOS, etc. also begin to provide support for USB2.0.

3.USB interface related problem set

● Does my hardware support USB interface?

When booting, enter the CMOS setting interface, and open the USB interface option (Enable) in the BIOS settings. If there are no relevant options, you need to upgrade the BIOS or explain that the motherboard does not support USB interface. The mainstream motherboards now provide support for USB interface.

● Does my operating system support USB interface?

Taking mainstream Windows as an example, check whether there are any related entries of "USB host controller" and "USB root hub" in "My Computer"-"Properties"-"Hardware"-"Device Manager"-"Universal Serial Bus Controller". If so, your operating system already supports USB interface. If not, it means that you need to upgrade and add USB interface driver or your operating system does not support USB interface. As shown in the following figure

● What if my motherboard doesn't have an integrated USB interface?

In this case, you can manually add a USB control card with PCI interface (generally 2 ~ 4 USB interfaces), just like installing a sound card or a video card, plug it in and install the corresponding driver.

How to make my USB keyboard work normally under DOS?

In order to make the keyboard (or mouse) with USB interface work normally under DOS, USB Legacy——Enable must be selected in CMOS setting interface to support the normal use of USB keyboard or mouse under DOS.

Because USB interface has some incomparable advantages over traditional interfaces, we can expect that USB will replace the parallel port, serial port and PS/2 interface used by keyboard and mouse and become a new generation of unified interface standard.

Four. IEEE 1394 interface

1. Introduction

When it comes to the booming USB interface, we can't help but mention its strong competitor-IEEE1394 interface.

If you have played DV, you must have heard of the word "firewire"-or Sony's "i.Link" and "IEEE 1394".

IEEE 1394 interface was first proposed by Apple (called "Firewire" technology), and was formally formulated as a bus standard by IEEE (Institute of Electrical and Electronics Engineers) in 1995. It has striking similarities with USB interface in appearance and most functions. At present, there are two versions of IEEE 1394, namely, the commonly used IEEE 1394a and the higher-speed IEEE 1394b under development.

IEEE 1394 usually has two interface modes, one is hexagonal six-pin interface and the other is quadrangular four-pin interface. The difference is that in addition to two pairs of data cables, the six-pin interface also has a pair of power cables, which can directly supply power to peripherals, mostly used for Macs and desktop computers, while the four-pin interface is mostly used for DV or notebook computers. If the data line of IEEE 1394 interface is stripped, we can see the internal structure as shown in the following figure:

2. Operating characteristics

● Simple and easy to use, supports hot plug, plug and play, and does not need to set device ID number. Because it is an operating system above Win98 SE, it has built-in IEEE 1394 support kernel and does not need to be driven.

The data transmission speed is low, IEEE 1394a is as high as 400Mbps, and the subsequent IEEE 1394b standard can increase the speed to 800Mbps, 1.6Gbps or even 3.2Gbps.

With its own power supply line, it can provide variable voltage of 8-40V, and the maximum allowable current is about1.5a. Therefore, it can supply power for equipment with low power consumption requirements.

● Real point-to-point connection, without distinction between master and slave devices, can directly realize data transmission between two DVs or multiple computers can share a DV player. Theoretically, we can directly save the image data in the DV player with IEEE 1394 interface to the hard disk with IEEE 1394 interface.

At present, the most widely used interface is IEEE 1394a interface with a bandwidth of 400Mbps. In contrast, the IEEE 1394b interface being developed can realize long-distance data transmission. At the beginning of this year, Texas Instruments introduced the industry's first IEEE 1394b device TSB8 1BA3, which not only doubled the speed of the previous generation 1394a to 800Mbps, but also increased the communication distance to 100 meters. If optical fiber with similar synchronization is used, the transmission speed can reach 65433. So as to ensure a better user experience in high-speed data transmission and multimedia networks.

V. Keyboard and Mouse Interface -PS/2

I believe that players have long since stopped using the mouse and keyboard of COM, right? Most of the mouse and keyboard we use now use PS/2 interface. The physical appearance of PS/2 interface of mouse and keyboard is exactly the same, and beginners often insert it wrongly, so that the industry has to use two different colors to distinguish it in PC'99 specification, but in fact their working principles are exactly the same, as can be seen from the definition of PS/2 interface pins below.

Note: 1+2 keyboard and mouse data signal 3 +5V (driving control chip and LED indicator) 4+5+ keyboard and mouse clock signal.