The RS-232 protocol
The RS-232 protocol Rs232 protocol transmission involves the sending of data one bit at a time, over a single communications line. In contrast, parallel communications require at least as many lines as there are bits in a word being transmitted (for an 8-bit word, a minimum of 8 lines are needed). RS232 Serial transmission is beneficial for long distance communications, whereas parallel is designed for short distances or when very high transmission rates are required. RS232 Standards One of the advantages of the RS232 protocol is that it lends itself to transmission over telephone lines. The serial digital data can be converted by modem, placed onto a standard voice-grade telephone line, and converted back to serial digital data at the receiving end of the line by another modem. Officially, RS-232 is defined as the "Interface between data terminal equipment and data communications equipment using serial binary data exchange." This definition defines data terminal equipment (DTE) as the computer, while data communications equipment (DCE) is the modem. A modem cable has pin-to-pin connections, and is designed to connect a DTE device to a DCE device. RS-232 is widely used for connections between data acquisition devices and computer systems. RS-232 devices are defined as either DTE (usually a computer) or DCE (usually an interface device). When wiring a DCE device to a computer (DTE), a straight-through connection is required. However, not all interface devices or data acquisition systems are DCE, therefore, require a null-modem cable, which 'crosses over' the necessary signal wires. Rs232 port In addition to communications between computer equipment over telephone lines, RS-232 protocol is now widely used for connections between data acquisition devices and computer systems. As in the definition of RS232, the computer is data transmission equipment (DTE). However, many interface products are not data communications equipment (DCE). Null modem cables are designed for this situation; rather than having the pinto- pin connections of modem cables, null modem cables have different internal wiring to allow DTE devices to communicate with one another. Cabling Options RS-232 cables are commonly available with either 4, 9 or 25-pin wiring. The 25-pin Rs232 cable connects every pin; the 9-pin Rs232 cables do not include many of the uncommonly used connections; 4-pin Rs232 cables provide the bare minimum connections, and have jumpers to provide "handshaking" for those devices that require it. These jumpers connect pins 4, 5 and 8, and also pins 6 and 20. The advent of the IBM PC AT has created a new wrinkle in RS-232 communications. Rather than having the standard 25-pin connector, this computer and many new expansion boards for pc's feature a 9-pin serial port. To connect this port to a standard 25- pin port, a 9- to 25-pin adaptor cable may be utilized, or the user may create his own cable specifically for that purpose. Selecting a Rs232 Cable The major considerations in choosing an RS-232 cable are based upon the devices to be connected. First, are you connecting two DTE devices (null modem cable) or a DTE device to a DCE device (modem cable)? Second, what connectors are required on each end, male or female, and 25 or 9-pin (AT style)? Usually, it is recommended that the user obtain the two devices to be connected, and then determine which cable is required. Wiring a Rs232 interface Most RS-232 devices will operate with only 3 signal wires: Transmit (TX), Receive (RX) and Ground (GND). In order for two RS-232 devices to communicate, you must connect the TX from one instrument to the RX of the second instrument, and vice versa. The Ground pins must be connected together. Keep in mind that a 25 pin RS-232 port on a PC trasmits on pin 2 and receives on pin 3, and Ground is pin 7. A 9-pin RS-232 port on a PC transmits on pin 3, receives on pin 2 and Ground is pin 5. You cannot simply connect two devices with a serial cable simply because the connectors fit. You must verify the functions of each pin on each device, as well as verify whether or not the cable is a straight-through or null-modem cable. RS485 Cable RS485 cable needs 3 conductors and a shield. Many people say it's a two-wire network but it is not. Two conductors are used to carry the RS485 Differential voltage signal. The Shield is connected to earth/ground at one end only and provides shielding against induced noise. Why Do You Need A Special Serial (USB-TTL) Cable to Debrick Your Router? First of all I recommend the USB-to-Serial Cable: 3.3V TTL cable that is available here. They come with different types of connectors Bare Wire, 6 Pin SIP and Audio Plug Connector. But the business end, the USB side is very different than a standard USB cable. The key to these cables are that each one contains a small internal electronic circuit board, utilizing the FT232R chip, which is encapsulated into the USB connector end of the cable. They use FTDI?’s FT232RQ USB to Serial UART interface IC device which handles all the USB signalling and protocols. These cables require USB drivers to make them work, but they are available free from us, which is then used to make the FT232R chip in the cable appear as a virtual COM port (VCP) on your computer. This allows you to communicate with the USB interface via a standard PC serial emulation port (for example TTY or PUTTY). What are typical transmission speeds for USB cables? Generally speaking, USB cable is classified into one of two different bandwidth groups: 1.1, which transfers data at a maximum rate of 1.5 Mbit per second, and 2.0, with a 480 Mbit per second data transfer rate. USB 2.0 is backward compatible with the lower data transmission requirements of 1.1, but the substitution can’t be reversed; 1.1 just can’t deliver the rate of data transfer that USB 2.0-rated devices need. In addition to the bandwidth classifications listed above, USB devices can also be labeled in the following “speed” categories, which specify the amount of bandwidth they need to operate: Low Speed: The “ low speed” rating indicates that a device requires minimal bandwidth (1.5 Mbit/s) to function, so it can be used in conjunction with either 1.1 or 2.0 USB cables. Joysticks, keyboards and computer mice are a few common examples of low speed devices. Full Speed: Devices labeled “full speed” need a signal rate of 12 Mbit per second. Since this is such a common bandwidth requirement, all USB hubs on the market have been designed to support Full Speed. And even though the data transfer speed is higher, Full Speed – like Low Speed – transmits equally well via 1.1 or 2.0 USB cables. High Speed: “ High speed” USB devices run at 480 Mbit per second, and require a 2.0-rated USB cable. What does it mean when USB cables and devices are described as “hot swappable?” One of the most convenient features of USB cable and devices is their ability to be “hot swapped,” which means that they can be plugged into – and unplugged from – a computer as needed, without that computer needing to be powered down first. The cable industry is a small but competitive place, with some companies making big claims about why its audio cable is better than others. We’ll take you through the cable components, claims, and myths to “cut through the noise” and explain when cables affect your sound. Conductor A cable’s conductor is the wire that conducts the electricity needed to pass signal and power. Conductors of appropriate size and material preserve the integrity of electrical transfer through the cable from the original source. Should the conductor be too small or made of inferior conductive metals, the audio signal will encounter more resistance and the sound will change. Conductive Materials Silver is the most conductive metal, which the human ear perceives as a brighter and more present sound. You don’t often see silver used in cables due mainly to its price. Copper is the second most conductive metal and most commonly used in cables When compared to silver, the human ear perceives copper as a more balanced and “warm” sound. To learn more and hear how silver and copper compare, check out our previous story, The Advantage of Silver Cable. Other common conductive metals for cables are gold and aluminum. Gold isn’t as conductive as silver or copper, and due to its cost, it’s never used as a primary conductor. Instead, gold is often used as a coating on cable connector ends, which we will cover below. Aluminum has much lower conductivity and is typically found in the most inexpensive audio cables, which lack the same clarity and brightness of sound，such as 2.5mm audio cable, 3.5mm audio cable and so on What is AS/NZS 3008? AS/NZS 3008.1.1 is an Australian/New Zealand standard which defines electrical properties (namely ampacity) of cables under typical Australian conditions and installation arrangements. It applies to Alternating Current (AC) systems up to and including 0.6/1.0 kV. Despite its title including ‘alternating voltages’, AS/NZS 3008 can also be applied to DC installations. AS/NZS 3008 is important because it allows us to size cables in a way that minimises system cost while still satisfying the following circuit requirements: Current-carrying capacity (CCC). Also known as ampacity, this is the maximum continuous current that a conductor can carry under its installation conditions without exceeding its rated temperature. An adequate CCC is required for all installations, otherwise cable damage and safety issues can occur. Voltage drop (Vd). Voltage drop is the decrease of voltage along the cable run due to the cable’s internal resistance. Voltage drops are undesirable because generated energy is lost as heat. Therefore, voltage drop must be considered when sizing PV cables to avoid degraded performance. Short-circuit temperature limit. This is the temperature that cables can adequately handle when exposed to their maximum prospective short circuit current. AS/NZS 5033:2014 sets out the calculation of prospective short circuit currents in PV systems. As PV systems are a current-limited source, this is not a limiting factor in DC cable selection. Ethernet Cables and How They Work An Ethernet cable is a common type of network cable used with wired networks. Ethernet cables connect devices such as PCs, routers, and switches within a local area network. These physical cables are limited by length and durability. If a network cable is too long or of poor quality, it won't carry a good network signal. These limits are one reason there are different types of Ethernet cables that are optimized to perform certain tasks in specific situations.
>http://www.sinetechcable.com/serial-communication-cable/rs232-cable/
Посмотреть всю страницу