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35-414: Before the advent of on-screen displays , the only interface available for programming a home video recorder was a small VFD , LED or LCD panel and a small number of buttons. Correctly setting up a recording for a specific program was therefore a somewhat complex operation for many people. G-Code, VideoPlus+ and ShowView were introduced in the late 1980s to remove this difficulty. The central concept of

70-607: A micromechanical resonator on the silicon chip of the RTC. This reduces the size and cost of an RTC by reducing its parts count. Micromechanical resonators are much more sensitive to temperature than quartz resonators. So, these compensate for temperature changes using an electronic thermometer and electronic logic. Typical crystal RTC accuracy specifications are from ±100 to ±20 parts per million (8.6 to 1.7 seconds per day), but temperature-compensated RTC ICs are available accurate to less than 5 parts per million. In practical terms, this

105-493: A real-time clock (RTC) was added to display time and date on video terminals (with greater performance in 1996). In the 1980s, OSD-capable TVs started to be more common, such as Zenith 's "System 3" series. Akai have been credited with the introduction of OSD in VCRs in the 1980s, including the introduction of on screen programming. By the mid-1990s, VCRs with these displays became widely available. This made it possible to reduce

140-438: A thermistor and analog-to-digital converter ) and uses a polynomial to calculate "rate" about once per minute. These require a calibration that measures the frequency at several temperatures, and then a linear regression to find the equation of temperature. The most common quartz crystals in a system are SC-cut crystals, and their rates over temperature can be characterized with a 3rd-degree polynomial. So, to calibrate these,

175-474: A second) is subtracted from "time", and the clock's timing-chain software is invoked to count fractions of seconds, seconds, etc. With 32- bit variables for time and rate, the mathematical resolution of "rate" can exceed one part per billion. The clock remains accurate because it will occasionally skip a fraction of a second, or increment by two fractions. The tiny skip (" jitter ") is imperceptible for almost all real uses of an RTC. The complexity with this system

210-774: Is an electronic device (most often in the form of an integrated circuit ) that measures the passage of time. Although the term often refers to the devices in personal computers , servers and embedded systems , RTCs are present in almost any electronic device which needs to keep accurate time of day . The term real-time clock is used to avoid confusion with ordinary hardware clocks which are only signals that govern digital electronics , and do not count time in human units. RTC should not be confused with real-time computing , which shares its three-letter acronym but does not directly relate to time of day. Although keeping time can be done without an RTC, using one has benefits: A GPS receiver can shorten its startup time by comparing

245-812: Is branded under different names depending on the country. It is known as VCR Plus+, VCR Plus+ Silver and VCR Plus+ Gold in the United States and Canada; G-Code in Japan, China, New Zealand and Australia; VideoPlus+ in Ireland, the United Kingdom, and Japan; and ShowView in the rest of Europe as well as in South Africa . The system is branded as VideoPlus+/ShowView in Europe due to an existing trademark registration for "VCR" by Philips in that continent, and as G-Code (the "G" standing for

280-437: Is converting dates and times to counts of seconds, but methods are well known. If the RTC runs when a unit is off, usually the RTC will run at two rates, one when the unit is on and another when off. This is because the temperature and power-supply voltage in each state is consistent. To adjust for these states, the software calculates two rates. First, software records the RTC time, reference time, on seconds and off seconds for

315-521: Is determining the instantaneous corrected value for the variable "rate". The simplest system tracks RTC time and reference time between two settings of the clock, and divides reference time by RTC time to find "rate". Internet time is often accurate to less than 20 milliseconds, so 8000 or more seconds (2.2 or more hours) of separation between settings can usually divide the forty milliseconds (or less) of error to less than 5 parts per million to get chronometer-like accuracy. The main complexity with this system

350-504: Is diagnostics if a television's display system is damaged. Without any external screens, it is almost impossible (without opening the TV) to determine the source of the error. TV accessories that depend heavily on OSDs, such as VCRs or DVD players, are also difficult to configure without the use of a TV. On older VCRs, it was possible to program recording timers without turning on the TV; a modern VCR requires

385-496: Is good enough to perform celestial navigation , the classic task of a chronometer . In 2011, chip-scale atomic clocks became available. Although vastly more expensive and power-hungry (120 mW vs. <1 μW), they keep time within 50 parts per trillion ( 5 × 10 ). Many integrated circuit manufacturers make RTCs, including Epson , Intersil , IDT , Maxim , NXP Semiconductors , Texas Instruments , STMicroelectronics and Ricoh . A common RTC used in single-board computers

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420-477: Is still uncommon. On-screen displays are also used in camcorders , and can display various information both on the viewfinder and on the TV set the camcorder is connected to. The complexity of graphics offered by such displays has greatly increased over the years, from simple monochrome images to intricate graphical user interfaces . Many computer monitors have an OSD menu for configuration. Several problems exist with regard to on-screen displays. One of them

455-519: Is the Maxim Integrated DS1307. The RTC was introduced to PC compatibles by the IBM PC/AT in 1984, which used a Motorola MC146818 RTC. Later, Dallas Semiconductor made compatible RTCs, which were often used in older personal computers , and are easily found on motherboards because of their distinctive black battery cap and silkscreened logo. A standard CMOS interface is available for

490-419: Is usually 32.768 kHz, the same frequency used in quartz clocks and watches . Being exactly 2 cycles per second, it is a convenient rate to use with simple binary counter circuits. The low frequency saves power, while remaining above human hearing range . The quartz tuning fork of these crystals does not change size much from temperature, so temperature does not change its frequency much. Some RTCs use

525-430: Is yet very repeatable (often less than 1 ppm). Software can do the math to make these into accurate RTCs. The hardware timer can produce a periodic interrupt, e.g. 50  Hz , to mimic a historic RTC (see below). However, it uses math to adjust the timing chain for accuracy: time = time + rate. When the "time" variable exceeds a constant, usually a power of two, the nominal, calculated clock time (say, for 1/50 of

560-798: The 1980s. The Akai VS-2 was the first VCR with an on-screen display, originally named the Interactive Monitor System. By displaying the information directly on the television screen, this innovation eliminated the need for the user to be physically near the VCR to program recording, read the tape counter, or perform other common features. Within a few years, all competing manufacturers had adopted on-screen display technology in their own products. Some computer software also uses OSDs, especially support programs for so-called "enhanced keyboards ", which often had additional medias like skipping through music tracks and volume adjustment. Their use outside this field

595-564: The IBM 360, the interrupt updates a 64-bit count of microseconds utilized by standardized systems software. The clock's jitter error is half if the clock interrupts for each zero crossing, instead of each cycle. The clock also usually formed the basis of computers' software timing chains; e.g. it was usually the timer used to switch tasks in an operating system. Counting timers used in modern computers provide similar features at lower precision, and may trace their requirements to this type of clock. (e.g. in

630-461: The PC RTC. In newer computer systems, the RTC is integrated into the southbridge chip. Some microcontrollers have a real-time clock built in, generally only the ones with many other features and peripherals . Some modern computers receive clock information by digital radio and use it to promote time-standards. There are two common methods: Most cell phone protocols (e.g. LTE ) directly provide

665-586: The VCR. The number is generated by an algorithm from the date, time and channel of the program; as a result, it does not rely on an over-the-air channel to serve as a conduit to ensure the recording is properly timed. This means it will not compensate for a disrupted schedule due to live sporting events or bulletins for breaking news events, however many video recorders with these systems also incorporate Programme Delivery Control (PDC) and use that to alter times if possible. The system has been licensed to television and VCR manufacturers in about 40 countries, but

700-653: The actual methods of efficient high-speed manufacturing are proprietary. Some computer designs such as smaller IBM System/360s , PDP-8s and Novas used a real-time clock that was accurate, simple and low cost. In Europe, North America and some other grids, the frequency of the AC mains is adjusted to the long-term frequency accuracy of the national standards. In those grids, clocks using AC mains can keep perfect time without adjustment. Such clocks are not practical in portable computers or grids (e.g. in South Asia) that do not regulate

735-491: The channel number and the time of day at the bottom of the screen. An OSD chip was added to the General instruments (GI) varactor tuning chip set designed in conjunction with RCA and Telefunken. The original OSD was merely to placate users who were faced with a snowy screen during auto tuning. Something the original architecture had not seen as an issue until it was first demonstrated. Once a display had been injected, at least in 1981,

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770-613: The current local time. If an internet radio is available, a computer may use the network time protocol . Computers used as local time servers occasionally use GPS or ultra-low frequency radio transmissions broadcast by a national standards organization (i.e. a radio clock ). The following system is well-known to embedded systems programmers, who sometimes must construct RTCs in systems that lack them. Most computers have one or more hardware timers that use timing signals from quartz crystals or ceramic resonators . These have inaccurate absolute timing (more than 100 parts per million) that

805-406: The current time, according to its RTC, with the time at which it last had a valid signal. If it has been less than a few hours, then the previous ephemeris is still usable. Some motherboards are made without RTCs. The RTC may be omitted out of desire to save money or reduce possible sources of hardware failure. RTCs often have an alternate source of power, so they can continue to keep time while

840-740: The decline in CRT -based TV sets and rise in LCD / plasma televisions has seen the use and availability of dedicated OSD devices decline, as it is more cost effective to integrate OSD functions inside the main graphics processor. Modern LCD television monitors usually incorporate only two or three integrated circuits. Examples of integrated circuits to perform dedicated OSD are MAX7456 and STV5730. Both operate with NTSC or PAL, mixing with an existing signal or self-generating. Both have slightly different capabilities. This can be done by PIC video superimposer too. Akai produced consumer video cassette recorders (VCR) during

875-460: The frequency is measured at four temperatures. The common tuning-fork-style crystals used in watches and many RTC components have parabolic (2nd-degree) equations of temperature, and can be calibrated with only 3 measurements. MEMS oscillators vary, from 3rd degree to fifth degree polynomials, depending on their mechanical design, and so need from four to six calibration measurements. Something like this approach might be used in commercial RTC ICs, but

910-501: The frequency of AC mains. These computers' power supplies use a transformer or resistor divider to produce a sine wave at logic voltages. This signal is conditioned by a zero crossing detector, either using a linear amplifier , or a schmitt trigger . The result is a square wave with single, fast edges at the mains frequency. This logic signal triggers an interrupt. The interrupt handler software usually counts cycles, seconds, etc. In this way, it can provide an entire clock and calendar. In

945-476: The past, most adjustments on TV sets were performed with analog controls such as potentiometers and switches. This was used more recently also in monochrome portable TVs. After remote controls were invented, digital adjustments became common. They needed an external display, which was LED , LCD , or VFD based. Including this display increased manufacturing costs. When electronics became more advanced, it became clear that adding some extra devices for an OSD

980-435: The primary source of power is off or unavailable. This alternate source of power is normally a lithium battery in older systems, but some newer systems use a supercapacitor , because they are rechargeable and can be soldered . The alternate power source can also supply power to battery backed RAM . Most RTCs use a crystal oscillator , but some have the option of using the power line frequency . The crystal frequency

1015-460: The size (and cost) of the VFD or LCD in the VCR. Eventually, as VCRs declined in popularity and prices fell, many manufacturers dropped the internal display completely, relying completely on the on-screen display. All DVD players also use on-screen displays. Many PAL television sets use the internal Teletext decoder's graphics rendering system to further reduce costs. More recently (as of about 2005),

1050-419: The system is a unique number, a PlusCode, assigned to each program, and published in television listings in newspapers and magazines (such as TV Guide ). To record a program, the code number is taken from the newspaper and input into the video recorder, which would then record on the correct channel at the correct time. The code could also be entered into a dedicated remote control device that would then control

1085-512: The system's developer, Gemstar) in Japan because VCR is not a common abbreviation there ("VTR," for videotape recorder, is used instead). Japan initially used the name Video Plus+ and later changed to G-Code, an example of this is the Victor (JVC) HR-880. Because television programming schedules are different, the coding has to be adjusted in each of the regions and recording equipment is not interchangeable. The actual algorithms used to encode and decode

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1120-475: The television guide values from and to their time representations were published in 1992, but only for six-digit codes or less. Source code for seven and eight digit codes was written in C and Perl and posted anonymously in 2003. On-screen display An on-screen display ( OSD ) is an image superimposed on a screen picture, commonly used by modern television sets , VCRs , and DVD players to display information such as volume, channel, and time. In

1155-407: The two intervals between the last three times that the clock is set. Using this, it can measure the accuracy of the two intervals, with each interval having a different distribution of on and off seconds. The rate math solves two linear equations to calculate two rates, one for on and the other for off. Another approach measures the temperature of the oscillator with an electronic thermometer, (e.g.

1190-491: The user to turn on the TV to do so. Usability is generally also decreased with OSDs, as it is necessary to control a multitude of parameters with a few buttons, where earlier, real analog controls with mechanical feedback were available. The drawbacks of using OSDs do not outweigh their main advantage of being more cost-efficient and allowing to design less separate physical tuning controls, which has led to their widespread use. Real-time clock A real-time clock ( RTC )

1225-409: Was cheaper than adding a second display device. TV screens had become much bigger and could display much more information than a small second display. OSDs display graphical information superimposed over the picture, which is done by synchronizing the reading from OSD video memory with the TV signal. Some of the first OSD-equipped televisions were introduced by RCA in the late 1970s, simply displaying

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