4255 查看數據表（PDF） - Allegro MicroSystems
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4255 Datasheet PDF : 8 Pages
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4255
8-BIT
MICROCONTROLLER
FUNCTIONAL DESCRIPTION (cont’d)
Table 2 — Microcontroller terminal descriptions
A4255CA A4255CLN
DIP
SSOP
1
1
2
2
3
3
4
4
5
5, 6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15, 16
15
17
16
18
17
19
18
20
Function
Input
Input
Input
Input
Power
Output
I/O
Output
Output
Output
Output
Output
Output
Power
Output
Input
Input
Input
Description
Mode select 1
Mode select 2
Step in
Reset
Ground
Monitor out
Shift clock
Serial data out
Strobe out
Phase B
PFD B
Phase A
PFD A
Supply
Osc/clock out
Osc/clock in
Direction control
Mode select 0
Comments, connections, etc.
Static and/or dynamic control of stepping mode
Static and/or dynamic control of stepping mode
Governs full-step rate (÷8 for A3955; ÷16 for A3957)
Resets DIR., MS2, MS1, and MS0 to 0000 (detent)
Logic power return
Signals full-step rotor alignment (active low)
Pull up for A3955; pull down for A3957
Shifts 8-bit serial data to 74HC595 serial input
Latches 8-bit data into 74HC595 (latch clock in)
Controls current direction in phase B
Phase B recirculation control
Controls current direction in phase A
Phase A recirculation control
(VDD) Recommended range: 4.5 V to 5.5 V
Crystal oscilator connection
Crystal oscillator connection/external clock input
Determines direction of step motor rotation
Static and/or dynamic control of stepping mode
Mode-select inputs
These three inputs (MS2, MS1, and MS0) determine
the stepping format, disable/enable motor power, and reset
the controller/sequencer. In conjunction with the direction
input, the mode inputs control the sixteen operating states
listed. Deactivating stepper power in any position except
‘detent’ (i.e., a single phase activated) results in the motor
rotor advancing, or retracting, from its intermediate
position and alignment with a natural (i.e., minimum-
reluctance flux field) orientation. The absolute position
may be affected by inertia, load, fractional position,
ringing, etc. and cannot be determined without feedback.
Phase currents must be maintained to immobilize the
rotor/load in any intermediate position.
Step (clock) input
The sequencer stepping-clock frequency is a multiple
of the actual stepping rate. The A3955 requires a step-
ping-clock input frequency equal to eight times the
intended stepping rate for the motor; the A3957 requires a
stepping clock rate that is sixteen times the actual stepping
rate of the motor. However, neither design necessitates
that the step frequency be varied should the operating
mode(s) be switched during operation. Shifting from one
stepping format does not mandate a simultaneous (and
equivalent) change in the clock frequency.
Using a 20 MHz crystal (maximum limit for the
A4255) allows a 50 kHz stepping clock for the A3955,
and this equates to 6 250 full steps per second (50 kHz/8).
For the A3957 this 50 kHz stepping clock translates to
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
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