Misplaced Pages

#417582

80-538: Beginning with its selection as the hard drive subsystem for the original IBM XT disk drive controllers supporting the ST-412 interface grew to become ubiquitous in the personal computer industry, The ST-412 interface and its variants were the de facto industry standard for personal computer hard disks until the advent and wider adoption of the IDE or ATA interface in the early 1990s. Both interfaces used MFM encoding;

160-404: A micro controller . To make the motor shaft turn, one electromagnet is first given power, which magnetically attracts the gear's teeth. When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. This means that when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one. From there

240-413: A permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor magnet and the stator electromagnets. Pulses move the rotor clockwise or anticlockwise in discrete steps. If left powered at a final step, a strong detent remains at that shaft location. This detent has a predictable spring rate and specified torque limit; slippage occurs if the limit is exceeded. If current

320-455: A position sensor for feedback . The step position can be rapidly increased or decreased to create continuous rotation, or the motor can be ordered to actively hold its position at one given step. Motors vary in size, speed, step resolution, and torque . Switched reluctance motors are very large stepping motors with a reduced pole count. They generally employ closed-loop commutators . Brushed DC motors rotate continuously when DC voltage

400-492: A 20-foot (6.1 m) cable length. The standard channel code for the ST-412 (and ST-506) is MFM with one data bit per transition for a data rate of 5 Mbit/s. The ST-412HP RLL variant averages 1.5 data bits per transition for a data rate of 7.5 Mbit/s. In the ST-506 interface, the drive connects to a controller card with two ribbon cables carrying signals, while a third cable provides power. The two signal cables are

480-401: A coil-end wire is by measuring the resistance. Resistance between common wire and coil-end wire is always half of the resistance between coil-end wires. This is because there is twice the length of coil between the ends and only half from center (common wire) to the end. A quick way to determine if the stepper motor is working is to short circuit every two pairs and try turning the shaft. Whenever

560-408: A controlled current in each winding rather than applying a constant voltage. Chopper drive circuits are most often used with two-winding bipolar motors, the two windings being driven independently to provide a specific motor torque CW or CCW. On each winding, a "supply" voltage is applied to the winding as a square wave voltage; example 8 kHz. The winding inductance smooths the current which reaches

640-692: A desktop case similar to that of the IBM PC. It weighs 32 pounds (15 kg) and is approximately 19.5 inches (50 cm) wide by 16 inches (41 cm) deep by 5.5 inches (14 cm) high. Similarly to the original IBM PC, the XT main board included a socket for the Intel 8087 floating point arithmetic coprocessor . This optional chip, when installed, greatly accelerated arithmetic for such applications as computer aided design or other software that required large amounts of arithmetical calculations. Only software that

720-421: A disadvantage: the mechanical drive (called the "head-disk assembly", or HDA) and the controller are effectively fused into a monolithic black box, so that if something goes wrong with the drive, it is nearly impossible to do anything about it—the data is usually irretrievably lost. With a separated controller and disk system like that of the ST-506 interface, sometimes the problem can be resolved by connecting

800-513: A few early IDE drives were just drives with an ST-412 interface attached to a controller board or chip. Ultimately all SCSI and ATA drives had built the controller into the drive, thereby eliminating the ST-506/412 interface in such models. From ST-506/ST-412 OEM manual. In the following tables, "~" denotes a negated (active low) signal. IBM Personal Computer XT The IBM Personal Computer XT (model 5160, often shortened to PC/XT )

880-457: A higher-than-normal resistance is felt, it indicates that the circuit to the particular winding is closed and that the phase is working. Bipolar motors have a pair of single winding connections per phase. The current in a winding needs to be reversed in order to reverse a magnetic pole, so the driving circuit must be more complicated, typically with an H-bridge arrangement (however there are several off-the-shelf driver chips available to make this

SECTION 10

#1732775564418

960-452: A large drive voltage with a low resistance and low inductance. With an L/R drive it is possible to control a low voltage resistive motor with a higher voltage drive simply by adding an external resistor in series with each winding. This will waste power in the resistors, and generate heat. It is therefore considered a low performing option, albeit simple and cheap. Modern voltage-mode drivers overcome some of these limitations by approximating

1040-427: A level according to the square wave duty cycle . Most often bipolar supply (+ and - ) voltages are supplied to the controller relative to the winding return. So 50% duty cycle results in zero current. 0% results in full V/R current in one direction. 100% results in full current in the opposite direction. This current level is monitored by the controller by measuring the voltage across a small sense resistor in series with

1120-521: A simple affair). There are two leads per phase, none is common. A typical driving pattern for a two coil bipolar stepper motor would be: A+ B+ A− B−. I.e. drive coil A with positive current, then remove current from coil A; then drive coil B with positive current, then remove current from coil B; then drive coil A with negative current (flipping polarity by switching the wires e.g. with an H bridge), then remove current from coil A; then drive coil B with negative current (again flipping polarity same as coil A);

1200-457: A sinusoidal voltage waveform to the motor phases. The amplitude of the voltage waveform is set up to increase with step rate. If properly tuned, this compensates the effects of inductance and back-EMF , allowing decent performance relative to current-mode drivers, but at the expense of design effort (tuning procedures) that are simpler for current-mode drivers. Chopper drive circuits are referred to as controlled current drives because they generate

1280-413: A stepper motor must reach their full rated current during each step. Winding inductance and counter-EMF generated by a moving rotor tend to resist changes in drive current, so that as the motor speeds up, less and less time is spent at full current—thus reducing motor torque. As speeds further increase, the current will not reach the rated value, and eventually the motor will cease to produce torque. This

1360-448: A stepper motor with a 1.7 by 1.7 inches (43 mm × 43 mm) faceplate and dimensions given in inches. The standard also lists motors with faceplate dimensions given in metric units. These motors are typically referred with NEMA DD, where DD is the diameter of the faceplate in inches multiplied by 10 (e.g., NEMA 17 has a diameter of 1.7 inches). There are further specifiers to describe stepper motors, and such details may be found in

1440-407: A synchronous AC motor with the number of poles (on both rotor and stator) increased, taking care that they have no common denominator. Additionally, soft magnetic material with many teeth on the rotor and stator cheaply multiplies the number of poles (reluctance motor). Modern steppers are of hybrid design, having both permanent magnets and soft iron cores . To achieve full rated torque, the coils in

1520-411: A third HD SLCT line was shortly added to the design; a fourth was added a not much later by redefining the reduced Write Current signal, needed only by very early drives, as HD SLCT 3. Once the heads are properly positioned and the appropriate head is selected, data is read or written serially through a set of pins in the data cable. The limited bandwidth of the data cable was not an issue at the time and

1600-411: Is MFM, so the absolute signal states are not significant: the data is represented in the timing of the state transitions, like in floppy disk systems. While up to four drives can share a control cable, each drive has its own dedicated data cable connecting it to the hard disk controller (HDC). Most HDCs supported only two drives. The control card translates requests for a particular track and sector from

1680-647: Is a quickly increasing current as a function of inductance. This reaches the V/R value and holds for the remainder of the pulse. Thus when controlled by a constant voltage drive, the maximum speed of a stepper motor is limited by its inductance since at some speed, the voltage U will be changing faster than the current I can keep up. In simple terms the rate of change of current is L / R (e.g. a 10 mH inductance with 2 ohms resistance will take 5 ms to reach approx 2/3 of maximum torque or around 24 ms to reach 99% of max torque). To obtain high torque at high speeds requires

SECTION 20

#1732775564418

1760-500: Is an expansion chassis using an identical case and power supply to the XT, but instead of a system board, provides a backplane with eight card slots. It connects to the main system unit using an Extender Card in the system unit and a Receiver Card in the Expansion Unit, connected by a custom cable. The 5161 shipped with a 10 MB hard drive, and had room for a second one. The Expansion Unit can also contain extra memory, but

1840-470: Is applied to their terminals. The stepper motor is known for its property of converting a train of input pulses (typically square waves) into a precisely defined increment in the shaft’s rotational position. Each pulse rotates the shaft through a fixed angle. Stepper motors effectively have multiple "toothed" electromagnets arranged as a stator around a central rotor, a gear-shaped piece of iron. The electromagnets are energized by an external driver circuit or

1920-490: Is half of the full step. What is commonly referred to as microstepping is often sine–cosine microstepping in which the winding current approximates a sinusoidal AC waveform. The common way to achieve sine-cosine current is with chopper-drive circuits. Sine–cosine microstepping is the most common form, but other waveforms can be used. Regardless of the waveform used, as the microsteps become smaller, motor operation becomes smoother, thereby greatly reducing resonance in any parts

2000-402: Is ideally driven by sinusoidal current. A full-step waveform is a gross approximation of a sinusoid, and is the reason why the motor exhibits so much vibration. Various drive techniques have been developed to better approximate a sinusoidal drive waveform: these are half stepping and microstepping. In this drive method only a single phase is activated at a time. It has the same number of steps as

2080-401: Is not the factor that limited the performance of the system. However, the unshielded cable can sometimes be susceptible to high levels of noise. Like a floppy drive interface, ST-506 moves the drive head one track at a time with a timed pulse, which cannot occur faster than the stepper motor can move the head. The ST-412 disk drive, among other improvements, added buffered seek capability to

2160-464: Is removed, a lesser detent still remains, holding shaft position against spring or other torque influences. Stepping can then be resumed while reliably being synchronized with control electronics. Permanent magnet stepper motors have simple DC switching electronics, a power-off detent, and no position readout. These qualities are ideal for applications such as paper printers, 3D printers , and robotics. Such applications track position simply by counting

2240-401: Is straightforward to measure with an oscilloscope). These figures can be helpful for more in-depth electronics design, when deviating from standard supply voltages, adapting third party driver electronics, or gaining insight when choosing between motor models with otherwise similar size, voltage, and torque specifications. A stepper's low-speed torque will vary directly with current. How quickly

2320-439: Is the measure of the torque produced by a stepper motor when it is operated without an acceleration state. At low speeds the stepper motor can synchronize itself with an applied step frequency, and this pull-in torque must overcome friction and inertia. It is important to make sure that the load on the motor is frictional rather than inertial as the friction reduces any unwanted oscillations. The pull-in curve defines an area called

2400-435: Is the number of pole pairs, and J r {\displaystyle J_{r}} is the rotor inertia in kg·m². The magnitude of the undesirable ringing is dependent on the back EMF resulting from rotor velocity. The resultant current promotes damping, so the drive circuit characteristics are important. The rotor ringing can be described in terms of damping factor . Stepper motors' nameplates typically give only

2480-507: Is the second computer in the IBM Personal Computer line, released on March 8, 1983. Except for the addition of a built-in hard drive and extra expansion slots, it is very similar to the original IBM PC model 5150 from 1981. IBM did not specify an expanded form of "XT" on the machine, press releases, brochures or documentation, but some publications expanded the term as " eXtended Technology " or just " eXTended ". The XT

ST-506/ST-412 - Misplaced Pages Continue

2560-619: The PC/XT from Xebec and for the PC/AT from Western Digital . As a consequence of IBM's endorsement, most of the drives in the 1980s were based on the ST-506. However, the complexity of the controller and cabling led to newer solutions like SCSI , and later, ATA (IDE). A few early SCSI drives were actually ST-506 drives with a SCSI to ST-506 controller on the bottom of the drive. Atari also used Adaptec ACB-4000A SCSI to ST-506 converter inside its own line of SH204/SH205 external ACSI drives. Likewise

2640-637: The XT/370 ; they had an additional (co-)processor board that could execute System/370 instructions. An XT-based machine with a Series/1 co-processor board existed as well, but it had its own System Unit number, the IBM 4950 . In 1986, the XT 286 (model 5162) was released with a 6 MHz Intel 80286 processor. Despite being marketed as a lower-tier model than the IBM AT , this system runs many applications faster than

2720-450: The ATs of the time with 6 MHz 286 processors, since it has zero- wait state RAM. It shipped with 640 KB RAM standard, an AT-style 1.2 MB high-density diskette drive and a 20 MB hard disk. Despite these features, reviews rated it as a poor market value. The XT 286 uses a 157-watt power supply, which can internally switch between 115 or 230 V AC operation. Both

2800-494: The Extender card inserts wait states for memory in the Expansion Unit, so it may be preferable to install memory into the main system unit. The 5161 can be connected to either an XT or to the earlier 5150 (the original IBM PC). PC DOS 2.0 offers a 9-sector floppy disk format, providing 180K/360K (single- vs. dual-sided) capacity per disk, compared to the 160K/320K provided by the 8-sector format of previous releases. The XT

2880-576: The IBM Model M, but in a modified variant that used the XT's keyboard protocol and lacked LEDs). Submodels 267, 277 and 088 had the original keyboard, but 3.5" floppy drives became available and 20MB Seagate ST-225 hard disks in 5.25" half-height size replaced the full-height 10 MB drives. Submodel 788 was the only XT sold with the Color Graphics Adapter as a standard feature. Submodels 568, 588, and 589 were used as basis for

2960-558: The XT. The 3270 PC , a variant of the XT featuring 3270 terminal emulation, was released in October 1983. Submodel 068 and 078, released in 1985, offered dual-floppy configurations without a hard drive as well, and the new Enhanced Graphics Adapter and Professional Graphics Adapter became available as video card options. In 1986, the 256–640 KB motherboard models were launched, which switched to half-height drives. Submodels 268, 278 and 089 came with 101-key keyboards (essentially

3040-401: The command interpretation off the controller card and onto the drive itself in order to improve performance is a common feature of later hard drive connection schemes, notably SCSI , with its rich command set, and the storage-focused IDE systems. IDE, in effect, is a system for extending the computer bus so the interface controller can be built into the drive unit rather than being plugged into

3120-419: The computer's backplane. This allows a single "controller" card—really just an interface card—to communicate with multiple dissimilar drives, while it also reduces latency and noise between the controller and drive hardware. Effectively, the roles are reversed: instead of the controller doing almost all of the complex processing and the drive just transferring encoded data between the magnetic disks and

3200-579: The controller and drive was derived from the Shugart Associates SA1000 interface, which was in turn based upon the floppy disk drive interface, thereby making disk controller design relatively easy. The ST-412 interface was adopted by numerous HDD manufacturers such that the interface became a de facto industry standard for disk drives well into the 1990s. The limitations of the ST-412 interface are 5 million transitions per second maximum on data lines, 16 heads, 4 drive units and

3280-499: The controller, the drive does almost all of the complex processing and the "controller" just transfers decoded data between the drive and the host system. In these systems, the operational details of the drive, like head selection and seeking, are entirely hidden from the host and handled within the drive's dedicated controller. These became known as "smart" drives, while ST-506–like devices retroactively became known as "dumb". While integrated controllers have many benefits, they also have

ST-506/ST-412 - Misplaced Pages Continue

3360-410: The cycle is complete and begins anew. Static friction effects using an H-bridge have been observed with certain drive topologies. Dithering the stepper signal at a higher frequency than the motor can respond to will reduce this "static friction" effect. Because windings are better utilized, they are more powerful than a unipolar motor of the same weight. This is due to the physical space occupied by

3440-526: The disk drive, containing the actual (perhaps very important) data, to another compatible controller. Furthermore, an ST-506 style interface makes it possible and easy not only to replace the controller without throwing away the data, but to get access to the analog data signals from the disk drive and process them through a special data recovery system that may be able to reconstruct data that a normal controller cannot read. Such data recovery techniques are much more difficult to execute on integrated drives, because

3520-473: The drive transistors in the right order, and this ease of operation makes unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements. For the experimenter, the windings can be identified by touching the terminal wires together in PM motors. If the terminals of a coil are connected, the shaft becomes harder to turn. One way to distinguish the center tap (common wire) from

3600-552: The electromagnets of other groups to form a uniform pattern of arrangement. For example, if the stepper motor has two groups identified as A or B, and ten electromagnets in total, then the grouping pattern would be ABABABABAB. Electromagnets within the same group are all energized together. Because of this, stepper motors with more phases typically have more wires (or leads) to control the motor. There are three main types of stepper motors: permanent magnet , variable reluctance , and hybrid synchronous. Permanent magnet motors use

3680-406: The full-step drive, but the motor will have significantly less torque than rated. It is rarely used. The animated figure shown above is a wave drive motor. In the animation, rotor has 25 teeth and it takes 4 steps to rotate by one tooth position. So there will be 25 × 4 = 100 steps per full rotation and each step will be 360 ⁄ 100 = 3.6 ° . This is the usual method for full-step driving

3760-466: The full-step position (where only a single phase is on). This may be mitigated by increasing the current in the active winding to compensate. The advantage of half stepping is that the drive electronics need not change to support it. In animated figure shown above, if we change it to half-stepping, then it will take 8 steps to rotate by 1 tooth position. So there will be 25×8 = 200 steps per full rotation and each step will be 360/200 = 1.8°. Its angle per step

3840-453: The host system into a sequence of head positioning commands, including setting the direction of head movement, in or out, and sending individual "STEP" commands to move. Four of the control cable pins, "HD SLCT 0" through "HD SLCT 3", allow the selection among up to 16 heads, although only four are available on the two-platter ST-506. The original ST-506/ST-412 interface defined only two HD SLCT lines, providing supporting for only four heads, but

3920-473: The interface. The controller sends the required STEP pulses to the drive as fast as it can receive them. The ST506 disk drive without buffered seek averages 170 ms (similar to a floppy drive or modern optical drive ) while the mechanically very similar ST-412 disk drive with buffered seek averages 85 ms. By the late 1980s, drives with an ST-412 interface were capable of average seek times between 15 and 30 milliseconds. The process of moving portions of

4000-436: The microstepping divisor number grows, step size repeatability degrades. At large step size reductions it is possible to issue many microstep commands before any motion occurs at all and then the motion can be a "jump" to a new position. Some stepper controller ICs use increased current to minimise such missed steps, especially when the peak current pulses in one phase would otherwise be very brief. A step motor can be viewed as

4080-432: The motor may be connected to, as well as the motor itself. Resolution will be limited by the mechanical stiction , backlash , and other sources of error between the motor and the end device. Gear reducers may be used to increase resolution of positioning. Step size reduction is an important step motor feature and a fundamental reason for their use in positioning. Example: many modern hybrid step motors are rated such that

SECTION 50

#1732775564418

4160-453: The motor. As the motor's rotor turns, a sinusoidal voltage is generated proportional to the speed (step rate). This AC voltage is subtracted from the voltage waveform available to induce a change in the current. L/R driver circuits are also referred to as constant voltage drives because a constant positive or negative voltage is applied to each winding to set the step positions. However, it is winding current, not voltage that applies torque to

4240-446: The motor. This kind of motor can be wired in several configurations: Multi-phase stepper motors with many phases tend to have much lower levels of vibration. While they are more expensive, they do have a higher power density and with the appropriate drive electronics are often better suited to the application . Stepper motor performance is strongly dependent on the driver circuit . Torque curves may be extended to greater speeds if

4320-440: The motor. Two phases are always on so the motor will provide its maximum rated torque. As soon as one phase is turned off, another one is turned on. Wave drive and single phase full step are both one and the same, with same number of steps but difference in torque. When half-stepping, the drive alternates between two phases on and a single phase on. This increases the angular resolution. The motor also has less torque (approx 70%) at

4400-413: The needed analog signals from the disk are not available at a standard interface and the internal data recording method, sector format, and disk organization of nearly every integrated drive model is different and secret. Many other companies quickly introduced drives using the same connectors and signals, creating a hard drive standard based on the ST-506. IBM chose to use it, acquiring adapter cards for

4480-414: The number of steps that each motor has been instructed to take. Variable reluctance (VR) motors have a soft iron rotor and operate based on the principle that minimum reluctance occurs with minimum gap, so the rotor points are attracted toward the stator's magnetic poles . Variable reluctance motors have detents when powered on, but not when powered off. Hybrid synchronous motors are a combination of

4560-716: The original XT and the XT/286 was discontinued in late 1987 after the launch of the IBM Personal System/2 (PS/2) line. The 8086-powered IBM PS/2 Model 30 served as the direct replacement for the XT in that PS/2 line. Unlike higher-end entries in the PS/2 line, which feature the Micro Channel expansion bus, the Model 30 contains 8-bit ISA bus slots, exactly like the XT. The XT was well received, although PC DOS 2.0

4640-441: The permanent magnet and variable reluctance types, to maximize power in a small size. There are two basic winding arrangements for the electromagnetic coils in a two phase stepper motor: bipolar and unipolar. A unipolar stepper motor has one winding with center tap per phase. Each section of windings is switched on for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without switching

4720-426: The polarity of the common wire, the commutation circuit can be simply a single switching transistor for each half winding. Typically, given a phase, the center tap of each winding is made common: three leads per phase and six leads for a typical two phase motor. Often, these two phase commons are internally joined, so the motor has only five leads. A microcontroller or stepper motor controller can be used to activate

4800-427: The problem by adding three extra expansion slots for a total of eight. While the slots themselves are identical to those in the original PC, the amount of physical space in the chassis differs, so two of the new slots (located behind the hard drive) cannot accept full-length cards. In addition, the spacing of the slots is narrower than in the original PC, making it impossible to install some multi-board cards. The 5161

4880-466: The process is repeated. Each of the partial rotations is called a "step", with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle. The circular arrangement of electromagnets is divided into groups, each group called a phase, and there is an equal number of electromagnets per group. The number of groups is chosen by the designer of the stepper motor. The electromagnets of each group are interleaved with

SECTION 60

#1732775564418

4960-406: The specifications) when not driven electrically. Soft iron reluctance cores do not exhibit this behavior. When the motor moves a single step it overshoots the final resting point and oscillates round this point as it comes to rest. This undesirable ringing is experienced as motor rotor vibration and is more pronounced in unloaded motors. An unloaded or under loaded motor may, and often will, stall if

5040-409: The start/stop region. Into this region, the motor can be started/stopped instantaneously with a load applied and without loss of synchronism. The stepper motor pull-out torque is measured by accelerating the motor to the desired speed and then increasing the torque loading until the motor stalls or misses steps. This measurement is taken across a wide range of speeds and the results are used to generate

5120-411: The stator poles can be reversed more quickly, the limiting factor being a combination of the winding inductance. To overcome the inductance and switch the windings quickly, one must increase the drive voltage. This leads further to the necessity of limiting the current that these high voltages may otherwise induce. An additional limitation, often comparable to the effects of inductance, is the back-EMF of

5200-411: The stepper motor shaft. The current I in each winding is related to the applied voltage V by the winding inductance L and the winding resistance R. The resistance R determines the maximum current according to Ohm's law I=V/R. The inductance L determines the maximum rate of change of the current in the winding according to the formula for an inductor dI/dt = V/L. The resulting current for a voltage pulse

5280-437: The stepper motor's dynamic performance curve. As noted below this curve is affected by drive voltage, drive current and current switching techniques. A designer may include a safety factor between the rated torque and the estimated full load torque required for the application. Synchronous electric motors using permanent magnets have a resonant position holding torque (called detent torque or cogging , and sometimes included in

5360-529: The subsequent extension of the ST-412 interface, the ST-412HP interface, used RLL encoding for a 50% increase in capacity and bit rate . The ST-506 HDD was the first 5.25 inch hard disk drive , introduced in 1980 by Shugart Technology (now Seagate Technology ). It stored up to 5 megabytes after formatting (153 cylinders, 4 heads, 32 sectors/track, 256 bytes/sector) and cost US$ 1,500 (equivalent to $ 5,547 in 2023). The similar, 10-megabyte ST-412 HDD

5440-819: The torque falls off at faster speeds depends on the winding inductance and the drive circuitry it is attached to, especially the driving voltage. Steppers should be sized according to published torque curve , which is specified by the manufacturer at particular drive voltages or using their own drive circuitry. Dips in the torque curve suggest possible resonances, whose impact on the application should be understood by designers. Step motors adapted to harsh environments are often referred to as IP65 rated. The US National Electrical Manufacturers Association (NEMA) standardises various dimensions, marking and other aspects of stepper motors, in NEMA standard (NEMA ICS 16-2001 ). NEMA stepper motors are labeled by faceplate size, NEMA 17 being

5520-416: The travel of every full step (example 1.8 degrees per full step or 200 full steps per revolution) will be within 3% or 5% of the travel of every other full step, as long as the motor is operated within its specified operating ranges. Several manufacturers show that their motors can easily maintain the 3% or 5% equality of step travel size as step size is reduced from full stepping down to 1/10 stepping. Then, as

5600-512: The vibration experienced is enough to cause loss of synchronisation. Stepper motors have a natural frequency of operation. When the excitation frequency matches this resonance the ringing is more pronounced, steps may be missed, and stalling is more likely. Motor resonance frequency can be calculated from the formula: where M h {\displaystyle M_{h}} is the holding torque in N·m, p {\displaystyle p}

5680-439: The video controller, disk controller and printer interface) each came as separate expansion cards and could quickly fill up all five available slots, requiring the user to swap cards in and out as tasks demanded. Some PC clones addressed this problem by integrating components into the motherboard to free up slots, while peripheral manufacturers produced products which integrated multiple functions into one card. The XT addressed

5760-436: The wide 34-pin control cable and the narrow 20-pin data cable . The control cable interface is very similar to the standard Shugart floppy disk interface; like that floppy disk interface, it can support four drives. The data cable carries a read signal and write signal, both as differential binary signals: the two signal states correspond to the two possible differential signal polarities. The data represented by these signals

5840-399: The winding current and occasionally the voltage and winding resistance. The rated voltage will produce the rated winding current at DC: but this is mostly a meaningless rating, as all modern drivers are current limiting and the drive voltages greatly exceed the motor rated voltage. Datasheets from the manufacturer often indicate Inductance. Back-EMF is equally relevant, but seldom listed (it

5920-431: The winding. This requires additional electronics to sense winding currents, and control the switching, but it allows stepper motors to be driven with higher torque at higher speeds than L/R drives. It also allows the controller to output predetermined current levels rather than fixed. Integrated electronics for this purpose are widely available. A stepper motor is a polyphase AC synchronous motor (see Theory below), and it

6000-435: The windings. A unipolar motor has twice the amount of wire in the same space, but only half used at any point in time, hence is 50% efficient (or approximately 70% of the torque output available). Though a bipolar stepper motor is more complicated to drive, the abundance of driver chips means this is much less difficult to achieve. An 8-lead stepper is like a unipolar stepper, but the leads are not joined to common internally to

6080-466: Was especially written to take advantage of the coprocessor would show a significant speedup. The power supply is 130 watts, an upgrade from the original PC. Those sold in the US were configured for 120 V AC only and could not be used with 240 V mains supplies. XTs with 240 V-compatible power supplies were later sold in international markets. Both were rated at 130 watts. IBM made several submodels of

6160-443: Was introduced in late 1981 (with 306 cylinders). The ST225 was introduced shortly thereafter with 20 megabytes and half the height. All three used MFM encoding, a widely used coding scheme. A subsequent extension of the ST-412 interface, the ST-412HP interface , used RLL encoding for a 50% increase in capacity and bit rate . The ST-506 drive connected to a computer system through a disk controller . The ST-506 interface between

6240-524: Was not offered in a floppy-only model for its first two years on the market, although the standard ribbon cable with two floppy connectors was still included. At that time, in order to get a second floppy drive, the user had to purchase the 5161 expansion chassis. Like the original PC, the XT came with IBM BASIC in ROM . The XT BIOS also displays a memory count during the POST , unlike the original PC. The XT has

6320-534: Was regarded as a greater improvement than any of the hardware changes, and by the end of 1983 IBM was selling every unit they made. By 1985 the IBM PC AT made the XT obsolete for most customers. Photo galleries: Stepper motor A stepper motor , also known as step motor or stepping motor , is a Brushless DC electric motor that rotates in a series of small and discrete angular steps. Stepper motors can be set to any given step position without needing

6400-465: Was regarded as an incremental improvement over the PC and a disappointment compared to the next-generation successor that some had anticipated. Compared to the original IBM PC, the XT has the following major differences: Otherwise the specifications are identical to the original PC. The number of expansion slots in the original IBM PC was a limiting factor for the product, since essential components (such as

#417582