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71-404: Made of silver grey plastic, it had a black matte area around the keyboard area. Most of the 63 rubber chiclet keys were grey, with some (the more important) keys in marine blue, and with white control and break keys. Each of the grey keys could produce any of five inputs: Upper and lower-case letters (or numbers and symbols), two graphic characters (similar to the graphic symbols of PETSCII ), and

142-554: A centronics compatible printer port , (supported by BASIC with LPRINT , LLIST and HCOPY , a "screen dump" command) and an expansion interface port. The expansion port connector also had signal lines for an RS232 serial connection which BASIC supported with several commands, but its main use was to connect a 5¼-inch floppy disk drive. On its left side the JR-200 had two DB-9 joystick connectors which could be connected to standard (Atari style) joysticks, which could be read by

213-467: A loopback capability used for testing. When enabled, signals are echoed back to the sender rather than being sent on to the receiver. If supported, the DTE can signal the local DCE (the one it is connected to) to enter loopback mode by setting Local Loop (LL, pin 18) to ON, or the remote DCE (the one the local DCE is connected to) to enter loopback mode by setting Remote Loop (RL, pin 21) to ON. The latter tests

284-426: A router ) as an alternative to monitoring over Ethernet. In RS-232, user data is sent as a time-series of bits . Both synchronous and asynchronous transmissions are supported by the standard. In addition to the data circuits, the standard defines a number of control circuits used to manage the connection between the DTE and DCE. Each data or control circuit only operates in one direction, that is, signaling from

355-486: A "high" or "low" signaling rate. The rates, as well as which device will select the rate, must be configured in both the DTE and DCE. The prearranged device selects the high rate by setting the Data Signal Rate Selector (DSRS, pin 23) signal to ON. Sometimes called Data Rate Select (DRS), this signal should not be confused with the more commonly used Data Set Ready (DSR, pin 6). Many DCE devices have

426-514: A 25-pin D-sub connector does not necessarily indicate an RS-232-C compliant interface. For example, on the original IBM PC, a male D-sub was an RS-232-C DTE port (with a non-standard current loop interface on reserved pins), but the female D-sub connector on the same PC model was used for the parallel "Centronics" printer port . Some personal computers put non-standard voltages or signals on some pins of their serial ports. The standard does not define

497-502: A BASIC keyword . Two keys, ALPHA and GRAPH , are used to switch back and forth between character and graphics modes. Holding down the CONTROL key while pressing any grey key produced a BASIC keyword. In total the JR-200 had 253 built-in characters. 96 letters, numbers and symbols, 5 Greek letters , 63 graphical symbols, 79 Japanese ( katakana ) symbols and 10 music and other symbols. All symbols formed in an 8x8 pixel matrix, and

568-409: A DTE to the attached DCE or the reverse. Because transmit data and receive data are separate circuits, the interface can operate in a full duplex manner, supporting concurrent data flow in both directions. The standard does not define character framing within the data stream or character encoding. The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for

639-681: A bezel. The first laptop to feature this style of chiclet keyboard was the Mitsubishi Pedion in 1997 (rebranded as the OmniBook Sojourn by Hewlett-Packard ). Sony popularized the chiclet keyboard in laptops with the release of the Vaio X505 in 2004. All of the computers listed are from the early home computer era, except the OLPC XO-1. RS-232 In telecommunications , RS-232 or Recommended Standard 232

710-453: A cable that connects the corresponding pins according to the table below. Cables with 9 pins on one end and 25 on the other are common. Manufacturers of equipment with 8P8C connectors usually provide a cable with either a DB-25 or DE-9 connector (or sometimes interchangeable connectors so they can work with multiple devices). Poor-quality cables can cause false signals by crosstalk between data and control lines (such as Ring Indicator ). If

781-421: A common ground limits RS-232 to applications with relatively short cables. If the two devices are far enough apart or on separate power systems, the local ground connections at either end of the cable will have differing voltages; this difference will reduce the noise margin of the signals. Balanced, differential serial connections such as RS-422 or RS-485 can tolerate larger ground voltage differences because of

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852-461: A few of the twenty signals specified in the standard, so connectors and cables with fewer pins are sufficient for most connections, more compact, and less expensive. Personal computer manufacturers replaced the DB-25M connector with the smaller DE-9M connector. This connector, with a different pinout (see Serial port pinouts ), is prevalent for personal computers and associated devices. Presence of

923-496: A given cable will not allow a data connection, especially if a gender changer is in use, a null modem cable may be necessary. Gender changers and null modem cables are not mentioned in the standard, so there is no officially sanctioned design for them. The following table lists commonly used RS-232 signals (called "circuits" in the specifications) and their pin assignments on the recommended DB-25 connectors (see Serial port pinouts for other commonly used connectors not defined by

994-401: A keypress is registered when the top layer is forced through a hole to touch the bottom layer. For every key, the conductive traces on the bottom layer are normally separated by a non-conductive gap. Electrical current cannot flow between them; the switch is open. However, when pushed down, conductive material on the underside of the top layer bridges the gap between those traces; the switch

1065-471: A large proportion of modern PCs are technically similar to chiclet keyboards. The rubber keys are replaced with rubber domes, and hard plastic keytops rest on top of these. Because the keytops are wider than the rubber domes, the keytops are not separated but align almost perfectly with only a minimal gap in between each other. The term "chiclet" has also been used to describe low-profile, low-travel scissor keyboards with simplified, flat keycaps separated by

1136-416: A maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the voltages available to the line driver circuit. Many RS-232 driver chips have inbuilt charge pump circuitry to produce the required voltages from a 3 or 5 volt supply. RS-232 drivers and receivers must be able to withstand indefinite short circuits to

1207-502: A maximum cable length, but instead defines the maximum capacitance that a compliant drive circuit must tolerate. A widely used rule of thumb indicates that cables more than 15 m (50 ft) long will have too much capacitance, unless special cables are used. By using low-capacitance cables, communication can be maintained over larger distances up to about 300 m (1,000 ft). For longer distances, other signal standards, such as RS-422 , are better suited for higher speeds. Since

1278-424: A reduced voltage. Some manufacturers therefore built transmitters that supplied +5 V and −5 V and labeled them as "RS-232 compatible". Later personal computers (and other devices) started to make use of the standard so that they could connect to existing equipment. For many years, an RS-232-compatible port was a standard feature for serial communications , such as modem connections, on many computers (with

1349-449: A short-range, point-to-point, low-speed wired data connection is fully adequate. The Electronic Industries Association (EIA) standard RS-232-C as of 1969 defines: The standard does not define such elements as the character encoding (i.e. ASCII , EBCDIC , or others), the framing of characters (start or stop bits, etc.), transmission order of bits, or error detection protocols. The character format and transmission bit rate are set by

1420-569: A small built-in speaker. On the back of the device there was a volume control potentiometer that controlled both the internal and external speaker. On the back of the device you could also find an eight-pin DIN connector for a cassette recorder with which you could load programs at 2400 bit/s. Then two connectors for video output, an RCA connector RF output and an eight-pins DIN connector that could output NTSC or RGB video . The JR-200UP variant outputs composite PAL and RGB. Two other connectors provided

1491-461: A specialized DTE called a bit error rate tester (or BERT). Some synchronous devices provide a clock signal to synchronize data transmission, especially at higher data rates. Two timing signals are provided by the DCE. Pin 15 is the transmitter clock (TCK), or send timing (ST); the DTE puts the next bit on the transmit data line (pin 2) when this clock transitions from OFF to ON (so it is stable during

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1562-418: A synchronization preamble to the receiver when they are re-enabled. The DTE asserts RTS to indicate a desire to transmit to the DCE, and in response the DCE asserts CTS to grant permission, once synchronization with the DCE at the far end is achieved. Such modems are no longer in common use. There is no corresponding signal that the DTE could use to temporarily halt incoming data from the DCE. Thus RS-232's use of

1633-462: A tone over a 5-octave range, and played them in the background while the BASIC program continued. Clever use of the three square wave voices could be used to generate a range of other sounds, such as explosions. A keystroke could be accompanied by an audible feedback signal. Audio was output from an RCA (Tulip) connector onto which an eight ohm speaker could be directly connected, but the JR-200 also had

1704-484: A weight reading, or a GPS receiver that periodically sends position, if no configuration via RS-232 is necessary). When only hardware flow control is required in addition to two-way data, the RTS and CTS lines are added in a 5-wire version. The EIA-232 standard specifies connections for several features that are not used in most implementations. Their use requires 25-pin connectors and cables. The DTE or DCE can specify use of

1775-632: Is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange , issued in 1997. Changes since Revision C have been in timing and details intended to improve harmonization with the CCITT standard ITU-T/CCITT V.24  [ de ] , but equipment built to the current standard will interoperate with older versions. Related ITU-T standards include V.24 (circuit identification) and ITU-T/CCITT V.28  [ de ] (signal voltage and timing characteristics). In revision D of EIA-232,

1846-416: Is a computer keyboard with keys that form an array of small, flat rectangular or lozenge-shaped rubber or plastic keys that look like erasers or " Chiclets ", a brand of chewing gum manufactured in the shape of small squares with rounded corners. It is an evolution of the membrane keyboard , using the same principle of a single rubber sheet with individual electrical switches underneath each key, but with

1917-403: Is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a DTE ( data terminal equipment ) such as a computer terminal or PC , and a DCE ( data circuit-terminating equipment or data communication equipment ), such as a modem . The standard defines the electrical characteristics and timing of signals,

1988-453: Is a signal sent from the DCE to the DTE device. It indicates to the terminal device that the phone line is ringing. In many computer serial ports, a hardware interrupt is generated when the RI signal changes state. Having support for this hardware interrupt means that a program or operating system can be informed of a change in state of the RI pin, without requiring the software to constantly "poll"

2059-542: Is also used to refer to scissor keyboards with superficially similar appearance. The term first appeared during the home computer era of the late 1970s to mid-1980s. The TRS-80 Color Computer , TRS-80 MC-10 , and Timex Sinclair 2068 were all described as having "chiclet keys". This style of keyboard has been met with a poor reception. John Dvorak wrote that it was "associated with $ 99 el cheapo computers". The keys on ZX Spectrum computers are "rubber dome keys" which were sometimes described as "dead flesh", while

2130-404: Is closed, current can flow, and a keypress is registered. All such keyboards are characterized by having each key surrounded (and held in place) by a perforated plate, so there is a space between the keys. Unlike the membrane keyboard, where the user presses directly onto the top membrane layer, this form of chiclet keyboard places a set of moulded rubber keys above this. With some key designs,

2201-840: Is faster, uses lower voltages, and has connectors that are simpler to connect and use. Disadvantages of USB compared to RS-232 are that USB is far less immune to electromagnetic interference (EMI) and that maximum cable length defined by standards is much shorter (15 meters for RS-232 versus 3–5 meters for USB, depending on the USB version and use of active cables). RS-232 cable lengths of 2000 meters are possible with appropriate line drivers. In fields such as laboratory automation or surveying, RS-232 devices continue to be used. Some types of programmable logic controllers , variable-frequency drives , servo drives , and computerized numerical control equipment are programmable via RS-232. Computer manufacturers have responded to this demand by re-introducing

Panasonic JR-200 - Misplaced Pages Continue

2272-529: Is used beyond the original purpose of interconnecting a terminal with a modem, successor standards have been developed to address the limitations. Issues with the RS-232 standard include: In the book PC 97 Hardware Design Guide , Microsoft deprecated support for the RS-232 compatible serial port of the original IBM PC design. Today, RS-232 has mostly been replaced in personal computers by USB for local communications. Advantages compared to RS-232 are that USB

2343-531: Is used by some older uninterruptible power supplies (UPSs) to signal a power failure state to the computer. Certain personal computers can be configured for wake-on-ring , allowing a computer that is suspended to answer a phone call. The Request to Send (RTS) and Clear to Send (CTS) signals were originally defined for use with half-duplex (one direction at a time) modems such as the Bell 202 . These modems disable their transmitters when not required and must transmit

2414-761: Is used for I/O and contains 128 bytes of RAM plus four kilobytes of ROM. A version of the JR-200 called the Panasonic JR-200U was developed for the North American and European markets and was announced in January 1983. The JR-200 did not use Microsoft BASIC , but its own dialect, one that was designed to be mostly compatible with Microsoft BASIC. JR-BASIC was a greatly extended BASIC, with, (for example) graphical commands such as COLOR , (which selected character color, background color and display mode) and PLOT which permitted direct addressing of

2485-476: The DE-9M connector on their computers or by making adapters available. RS-232 ports are also commonly used to communicate to headless systems such as servers , where no monitor or keyboard is installed, during boot when an operating system is not yet running and therefore no network connection is possible. A computer with an RS-232 serial port can communicate with the serial port of an embedded system (such as

2556-474: The BASIC STICK command. In contrast to most other home computers of the time the JR-200 did not use an external transformer unit but had a built-in, completely contained, power supply. The computer received favorable reviews on its launch. Creative Computing wrote "The Panasonic JR-200 is one of the nicest new computers to make the scene in some time." Chiclet keyboard A chiclet keyboard

2627-561: The D-subminiature connector was formally included as part of the standard (it was only referenced in the appendix of RS-232-C). The voltage range was extended to ±25 volts, and the circuit capacitance limit was expressly stated as 2500 pF. Revision E of EIA-232 introduced a new, smaller, standard D-shell 26-pin "Alt A" connector, and made other changes to improve compatibility with CCITT standards V.24, V.28 and ISO 2110. Specification document revision history: Because RS-232

2698-407: The DTE. Unlike the original use of RTS and CTS with half-duplex modems, these two signals operate independently from one another. This is an example of hardware flow control . However, "hardware flow control" in the description of the options available on an RS-232-equipped device does not always mean RTS/CTS handshaking. Equipment using this protocol must be prepared to buffer some extra data, since

2769-593: The JR-200 could display 32 characters per line and 24 lines. All relevant keys would auto-repeat when pressed continuously. The JR-200 used a very unusual 8-bit CPU , the MN1800A , which was compatible with the Motorola MC6802 , a slightly improved version of the Motorola 6800 . It ran at a slow 0.89 MHz (according to unconfirmed information). There is also a second processor, the 4-bit MN1544CJR, which

2840-603: The MN1544CJR I/O chip, with three of the timer outputs being hooked up to generate square wave tones. The BASIC supported the sound capabilities with commands ranging from a simple BEEP command ( BEEP 1 producing an 880 Hz "middle octave A" sound), to the SOUND (f, d) command which took two numerical parameters for frequency and duration, and the PLAY and TEMPO commands which could take multiple commands to play

2911-460: The ON to OFF transition when the DCE registers the bit). Pin 17 is the receiver clock (RCK), or receive timing (RT); the DTE reads the next bit from the receive data line (pin 3) when this clock transitions from ON to OFF. Alternatively, the DTE can provide a clock signal, called transmitter timing (TT, pin 24) for transmitted data. Data is changed when the clock transitions from OFF to ON, and read during

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2982-409: The ON to OFF transition. TT can be used to overcome the problem of propagation delay in a long cable. ST must traverse a cable of unknown length and delay, clock a bit out of the DTE after another unknown delay, and return it to the DCE over the same unknown cable delay. When sending data at high speed, the data bit may not arrive in time for the ON to OFF transition of ST. Since the relation between

3053-421: The RS-232 device, can send data onto the bus. Modern communications environments use full-duplex (both directions simultaneously) modems. In that environment, DTEs have no reason to deassert RTS. However, due to the possibility of changing line quality, delays in processing of data, etc., there is a need for symmetric, bidirectional flow control . A symmetric alternative providing flow control in both directions

3124-414: The RS-232 interface, and provide sufficient current to comply with the slew rate requirements for data transmission. Because both ends of the RS-232 circuit depend on the ground pin being zero volts, problems will occur when connecting machinery and computers where the voltage between the ground pin on one end, and the ground pin on the other is not zero. This may also cause a hazardous ground loop . Use of

3195-798: The RS-232 standard was once a standard feature of many types of computers. Personal computers used them for connections not only to modems, but also to printers , computer mice , data storage, uninterruptible power supplies , and other peripheral devices. Compared with later interfaces such as RS-422 , RS-485 and Ethernet , RS-232 has lower transmission speed, shorter maximum cable length, larger voltage swing, larger standard connectors, no multipoint capability and limited multidrop capability. In modern personal computers, USB has displaced RS-232 from most of its peripheral interface roles. Thanks to their simplicity and past ubiquity, however, RS-232 interfaces are still used—particularly in industrial CNC machines, networking equipment and scientific instruments where

3266-454: The RTS and CTS signals, per the older versions of the standard, is asymmetric. This scheme is also employed in present-day RS-232 to RS-485 converters. RS-485 is a multiple-access bus on which only one device can transmit at a time, a concept that is not provided for in RS-232. The RS-232 device asserts RTS to tell the converter to take control of the RS-485 bus so that the converter, and thus

3337-399: The addition of an additional upper layer which provides superior tactile feedback through a buckling mechanism. The term "chiclet keyboard" is sometimes incorrectly used to refer to island-style keyboards . Since the mid-1980s, chiclet keyboards have been mainly restricted to lower-end electronics, such as small handheld calculators , cheap PDAs and many remote controls , though the name

3408-400: The circuit. The "sudden collapse" of the chiclet keyboard (along with the movement of the key) provides a greater tactile feedback to the user than a simple flat membrane keyboard. Most often the tops of the keys were hard, but sometimes they were made of the same material as the rubber dome itself. Other versions of the chiclet keyboard omit the upper membrane and hole/spacer layers; instead

3479-403: The communications link, as well as both DCEs. When the DCE is in test mode, it signals the DTE by setting Test Indicator (TI, pin 25) to ON. A commonly used version of loopback testing does not involve any special capability of either end. A hardware loopback is simply a wire connecting complementary pins together in the same connector (see loopback ). Loopback testing is often performed with

3550-457: The computer acting as the DTE). It remained in widespread use into the late 1990s. In personal computer peripherals, it has largely been supplanted by other interface standards, such as USB. RS-232 is still used to connect older designs of peripherals, industrial equipment (such as PLCs ), console ports, and special purpose equipment. The standard has been renamed several times during its history as

3621-403: The data transmission and the control signal lines. Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts with respect to the "Common Ground" (GND) pin; consequently, the range between −3 and +3 volts is not a valid RS-232 level. For data transmission lines (TxD, RxD, and their secondary channel equivalents), logic one is represented as a negative voltage and

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3692-610: The differential signaling. Unused interface signals terminated to the ground will have an undefined logic state. Where it is necessary to permanently set a control signal to a defined state, it must be connected to a voltage source that asserts the logic 1 or logic 0 levels, for example with a pull-up resistor . Some devices provide test voltages on their interface connectors for this purpose. RS-232 devices may be classified as Data Terminal Equipment (DTE) or Data Circuit-terminating Equipment (DCE); this defines at each device which wires will be sending and receiving each signal. According to

3763-516: The feel of the IBM PCjr 's chiclet keyboard was reportedly compared to "massaging fruit cake". Its quality was such that an amazed Tandy executive, whose company had previously released a computer with a similarly unpopular keyboard, asked "How could IBM have made that mistake with the PCjr?" Chiclet keyboards operate under essentially the same mechanism as in the membrane keyboard . In both cases,

3834-417: The ground or to any voltage level up to ±25 volts. The slew rate , or how fast the signal changes between levels, is also controlled. Because the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels. These also protect the device's internal circuitry from short circuits or transients that may appear on

3905-495: The low resolution graphics mode (64×48, using text semigraphics characters, which represented pixel blocks that used one-quarter of each character). Eight colors were available for the background and foreground use: blue, red, magenta, green, cyan, yellow, white and black. By re-programming a part of the character-set a limited high resolution graphics mode was achievable with a resolution of 256×192. The BASIC also supported on-screen editing and direct execution of BASIC instructions.

3976-419: The machine came with 32K of RAM, and had 30,716 bytes free for a Basic program. User memory could be expanded to 40K. JR-BASIC itself occupied 16K of ROM, while the character set video memory and I/O used another 6K. The JR-200 ROM also contained a machine code monitor to enter and execute machine code programs. The JR-200 was capable of producing a wide range of sounds. The JR-200 had a general purpose timer,

4047-442: The meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange , issued in 1997. The RS-232 standard had been commonly used with serial ports and serial cables . It is still widely used in industrial communication devices. A serial port complying with

4118-430: The original DCEs were (usually) modems. When electronic terminals (smart and dumb) began to be used, they were often designed to be interchangeable with teletypewriters, and so supported RS-232. Because the standard did not foresee the requirements of devices such as computers, printers, test instruments, POS terminals , and so on, designers implementing an RS-232 compatible interface on their equipment often interpreted

4189-405: The remote system may have begun transmitting just before the local system de-asserts RTR. A minimal "3-wire" RS-232 connection consisting only of transmit data, receive data, and ground, is commonly used when the full facilities of RS-232 are not required. Even a two-wire connection (data and ground) can be used if the data flow is one way (for example, a digital postal scale that periodically sends

4260-400: The same pin as RTS (Request to Send), and that when 133 is in use, RTS is assumed by the DCE to be asserted at all times. In this scheme, commonly called "RTS/CTS flow control" or "RTS/CTS handshaking" (though the technically correct name would be "RTR/CTS"), the DTE asserts RTS whenever it is ready to receive data from the DCE, and the DCE asserts CTS whenever it is ready to receive data from

4331-566: The serial port hardware, typically a UART , which may also contain circuits to convert the internal logic levels to RS-232 compatible signal levels. The standard does not define bit rates for transmission, except that it says it is intended for bit rates lower than 20,000 bits per second. RS-232 was first introduced in 1960 by the Electronic Industries Association (EIA) as a Recommended Standard . The original DTEs were electromechanical teletypewriters , and

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4402-439: The signal condition is called "mark". Logic zero is signaled with a positive voltage and the signal condition is termed "space". Control signals have the opposite polarity: the asserted or active state is positive voltage and the de-asserted or inactive state is negative voltage. Examples of control lines include request to send (RTS), clear to send (CTS), data terminal ready (DTR), and data set ready (DSR). The standard specifies

4473-496: The sponsoring organization changed its name, and has been variously known as EIA RS-232, EIA 232, and, most recently as TIA 232. The standard continued to be revised and updated by the Electronic Industries Association and since 1988 by the Telecommunications Industry Association (TIA). Revision C was issued in a document dated August 1969. Revision D was issued in 1986. The current revision

4544-553: The standard definitions are not always correctly applied, it is often necessary to consult documentation, test connections with a breakout box , or use trial and error to find a cable that works when interconnecting two devices. Connecting a fully standard-compliant DCE device and DTE device would use a cable that connects identical pin numbers in each connector (a so-called "straight cable"). " Gender changers " are available to solve gender mismatches between cables and connectors. Connecting devices with different types of connectors requires

4615-411: The standard idiosyncratically. The resulting common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of breakout boxes , patch boxes, test equipment, books, and other aids for the connection of disparate equipment. A common deviation from the standard was to drive the signals at

4686-440: The standard). The signals are named from the standpoint of the DTE. The ground pin is a common return for the other connections, and establishes the "zero" voltage to which voltages on the other pins are referenced. The DB-25 connector includes a second "protective ground" on pin 1; this is connected internally to equipment frame ground, and should not be connected in the cable or connector to signal ground. Ring Indicator (RI)

4757-585: The standard, male connectors have DTE pin functions, and female connectors have DCE pin functions. Other devices may have any combination of connector gender and pin definitions. Many terminals were manufactured with female connectors but were sold with a cable with male connectors at each end; the terminal with its cable satisfied the recommendations in the standard. The standard recommends the D-subminiature 25-pin connector up to revision C, and makes it mandatory as of revision D. Most devices only implement

4828-492: The state of the pin. RI does not correspond to another signal that carries similar information the opposite way. On an external modem the status of the Ring Indicator pin is often coupled to the "AA" (auto answer) light, which flashes if the RI signal has detected a ring. The asserted RI signal follows the ringing pattern closely, which can permit software to detect distinctive ring patterns. The Ring Indicator signal

4899-420: The underside of the rubber keys themselves have a conductive coating. When the key is pushed, the conductive underside makes contact with the traces on the bottom layer, and bridges the gap between them, thus completing the circuit. Grooves between hollow domes on the blue underside permit air to flow out of a dome when a key is pressed, and let air come back in when released. The dome switch keyboards used with

4970-405: The user pushes the key, and under sufficient pressure the thin sides of the rubber key suddenly collapse. In other designs — such as that seen in the diagram — the deliberate weak point is where the key joins the rest of the sheet. The effect is similar in both cases. This collapse allows the solid rubber center to move downwards, forcing the top membrane layer against the bottom layer, and completing

5041-463: Was developed and marketed in the late 1980s by various equipment manufacturers. It redefined the RTS signal to mean that the DTE is ready to receive data from the DCE. This scheme was eventually codified in version RS-232-E (actually TIA-232-E by that time) by defining a new signal, "RTR (Ready to Receive)", which is CCITT V.24 circuit 133. TIA-232-E and the corresponding international standards were updated to show that circuit 133, when implemented, shares

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