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參數(shù)資料
| 型號： | 4255 |
| 廠商： | Allegro MicroSystems, Inc. |
| 英文描述： | OSC 5V 14PIN TTL |
| 中文描述： | 8位微控制器 |
| 文件頁數(shù)： | 6/8頁 |
| 文件大?。?/td> | 142K |
| 代理商： | 4255 |
4255
8-BIT
MICROCONTROLLER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Direction control outputs
Two of the microcontroller outputs are devoted to
direction control. The direction signals follow the se-
quencing to provide the 1/8th-step ‘sinusoidal’ wave-
forms. Direction outputs are parallel, and connected
directly to the power IC inputs (A3955 in the schematic).
Obviously, both direction signals must coincide with the
8-bit serial-to-parallel conversion signals that control the
phase current ratios (D2, D1, and D0).
PFD control outputs
Another pair of microcontroller outputs constitute
parallel, direct control of the recirculation paths during
each PWM current cycle. The percentage of fast-decay
(or four-quadrant) to slow-decay (or two-quadrant)
recirculation determines how effectively the output current
tracks a sinusoidal waveform. Mixed-mode operation was
utilized for those portions of each microstepping cycle in
which the current is decreasing. The application of
mixed-mode decay allows the PWM current to properly
decay during each fixed-off-time interval.
The typical application shown includes a pair of
49.9 k
variables and allows setting the ratios of fast- and
slow-decay to match the individual characteristics of the
step motor, step frequency, supply voltage, etc. As the
stepping frequency is increased, waveform anomalies
become more pronounced, and the benefit of mixed mode
(or fast decay) also becomes very noticeable.
A comprehensive discussion of mixed-mode operation
is included in Allegro Technical Paper STP 97-5.
Oscillator input/clock input
This device connection serves as one terminal for a
parallel-cut crystal (oscillator 2 is the other). In the
typical application, two 20 pF capacitors are recommend-
ed, and a series resistor from oscillator out may be re-
quired if AT-cut crystals are utilized.
Also, this terminal is used if an external clock (from a
system computer, etc.) is connected here in lieu of a
crystal or ceramic resonator. If so, the oscillator out
connection is left open. The 20 MHz frequency limit
applies to using any clock source.
Oscillator output/clock output
This is the other device connection used for the
internal crystal oscillator (or ceramic resonator) that
supplies the microcontroller with an oscillator/time base
(
≤20 MHz).
Direction input
This input controls the sequencing of the winding
currents. Reversing direction may necessitate deceleration
(perhaps full stop) to avoid problems associated with the
load inertia causing the motor to overshoot the proposed
stop/reverse position.
A more extensive discussion of this microcontoller
and microstepping is included in Allegro Technical Paper
STP 99-11.
CONTROL OF PHASE CURRENTS
The power-driver ICs regulate the winding currents,
and the user establishes the design value via a stable
voltage reference and a current-sensing resistor for each
winding (R8 and R19).
FUNCTIONAL DESCRIPTION (cont’d)
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