Random access memory (RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in bursts, although the name DRAM / RAM has stuck. However, many types of SRAM, ROM, OTP, and NOR flash are still random access even in a strict sense. RAM is often associated with volatile types of memory (such as DRAM memory modules), where its stored information is lost if the power is removed. Many other types of non-volatile memory are RAM as well, including most types of ROM and a type of flash memory called NOR-Flash. The first RAM modules to come into the market were created in 1951 and were sold until the late 1960s and early 1970s.
MY ELECTRONICS
Friday, March 23, 2012
Sunday, March 18, 2012
ROM
Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates).
In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. Despite the simplicity, speed and economies of scale of mask ROM, field-programmability often make reprogrammable memories more flexible and inexpensive. As of 2007[update], actual ROM circuitry is therefore mainly used for applications such as microcode, and similar structures, on various kinds of digital processors (i.e. not only CPUs).
Other types of non-volatile memory such as erasable programmable read only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM or Flash ROM) are sometimes referred to, in an abbreviated way, as "read-only memory" (ROM), but this is actually a misnomer because these types of memory can be erased and re-programmed multiple times.[1] When used in this less precise way, "ROM" indicates a non-volatile memory which serves functions typically provided by mask ROM, such as storage of program code and nonvolatile data.
In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. Despite the simplicity, speed and economies of scale of mask ROM, field-programmability often make reprogrammable memories more flexible and inexpensive. As of 2007[update], actual ROM circuitry is therefore mainly used for applications such as microcode, and similar structures, on various kinds of digital processors (i.e. not only CPUs).
Other types of non-volatile memory such as erasable programmable read only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM or Flash ROM) are sometimes referred to, in an abbreviated way, as "read-only memory" (ROM), but this is actually a misnomer because these types of memory can be erased and re-programmed multiple times.[1] When used in this less precise way, "ROM" indicates a non-volatile memory which serves functions typically provided by mask ROM, such as storage of program code and nonvolatile data.
Friday, March 16, 2012
Wednesday, February 29, 2012
Timer IC 555
555 timer IC
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Introduced in 1971 by Signetics, the 555 is still in widespread use, thanks to its ease of use, low price and good stability, and is now made by many companies in the original bipolar and also in low-power CMOS types. As of 2003, it was estimated that 1 billion units are manufactured every year.
Design
The IC was designed in 1971 by Hans R. Camenzind under contract to Signetics, which was later acquired by Philips.Depending on the manufacturer, the standard 555 package includes 25 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8).Variants available include the 556 (a 14-pin DIP combining two 555s on one chip), and the two 558 & 559s (both a 16-pin DIP combining four slightly modified 555s with DIS & THR connected internally, and TR is falling edge sensitive instead of level sensitive). There is no 557.
The NE555 parts were commercial temperature range, 0 °C to +70 °C, and the SE555 part number designated the military temperature range, −55 °C to +125 °C. These were available in both high-reliability metal can (T package) and inexpensive epoxy plastic (V package) packages. Thus the full part numbers were NE555V, NE555T, SE555V, and SE555T. It has been hypothesized that the 555 got its name from the three 5 kΩ resistors used within, but Hans Camenzind has stated that the number was arbitrary.
Low-power versions of the 555 are also available, such as the 7555 and CMOS TLC555. The 7555 is designed to cause less supply glitching than the classic 555 and the manufacturer claims that it usually does not require a "control" capacitor and in many cases does not require a decoupling capacitor on the power supply. Such a practice should nevertheless be avoided, because noise produced by the timer or variation in power supply voltage might interfere with other parts of a circuit or influence its threshold voltages.
Monday, February 27, 2012
Autotransformer
An autotransformer is an electrical transformer with only one winding. The auto prefix refers to the single coil acting on itself rather than any automatic mechanism. In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps
where electrical connections are made. An autotransformer can be
smaller, lighter and cheaper than a standard dual-winding transformer
however the autotransformer does not provide electrical isolation.
Autotransformers are often used to step up or down between voltages in the 110-117-120 volt range and voltages in the 220-230-240 volt range, e.g., to output either 110 or 120V (with taps) from 230V input, allowing equipment from a 100 or 120V region to be used in a 230V region.
One end of the winding is usually connected in common to both the voltage source and the electrical load.
The other end of the source and load are connected to taps along the
winding. Different taps on the winding correspond to different voltages,
measured from the common end. In a step-down transformer the source is
usually connected across the entire winding while the load is connected
by a tap across only a portion of the winding. In a step-up transformer,
conversely, the load is attached across the full winding while the
source is connected to a tap across a portion of the winding.
As in a two-winding transformer, the ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they connect to. For example, connecting the load between the middle and bottom of the autotransformer will reduce the voltage by 50%. Depending on the application, that portion of the winding used solely in the higher-voltage (lower current) portion may be wound with wire of a smaller gauge, though the entire winding is directly connected.
Autotransformers are often used to step up or down between voltages in the 110-117-120 volt range and voltages in the 220-230-240 volt range, e.g., to output either 110 or 120V (with taps) from 230V input, allowing equipment from a 100 or 120V region to be used in a 230V region.
Operation
As in a two-winding transformer, the ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they connect to. For example, connecting the load between the middle and bottom of the autotransformer will reduce the voltage by 50%. Depending on the application, that portion of the winding used solely in the higher-voltage (lower current) portion may be wound with wire of a smaller gauge, though the entire winding is directly connected.
Sunday, February 12, 2012
Sunday, January 29, 2012
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