Little Step-U
Unipolar Stepper motor controller
TLA Microsystems Ltd
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Features
• Unipolar motors to 35V, 3.0A
• Full step, half step and wave drive modes • 1-5,000 steps per second
• Inbuilt speed ramp (0.1-20.0 seconds)• Simple serial commands (TTL interface)• Separate power input for motor and logic • Suitable for direct and L/R operation in all modes
• On board clamping diodes
• Current position register (+/-100,000,000)• Zero position and user marker registers • Absolute & Relative movement commands • Busy output
• Two inputs suitable for optical stops
• Slave mode using inputs for STEP & DIR •
Stop with motor coils on or off
Description
The Little Step-U  is a complete, serially controlled, drive system for unipolar stepper motors.  Using an intelligent module allows the host system to concentrate on the task at hand while the Little Step-U  performs all calculations and operation of the motor.
The desired operating speed, ramp time and drive mode can be configured once and then a single command used as required, to move to fixed or relative positions.  While the motor is in motion, a BUSY output is active and the movement can be optionally interrupted by one of the two external input
s.  The position of the motor is maintained in a readable register which can be set to zero (Home) by a command or when an input is activated.  A similar register is available to save a second position (Mark) either by command or from an input.  These points can then be referenced directly with a 'Move to home' or 'Move to mark' command.
A built-in ramping function accelerates the motor from a standstill to the desired speed over a specified time period, allowing faster final speeds to be achieved, and also to decelerate the motor to give maximum load braking.  When the motor is stopped, a command specifies whether the windings are left energized (for maximum holding torque) or turned off (for lower power consumption / dissipation).
A remote function is included for use in more complex systems.  Once activated, the two external inputs become STEP and DIR, with the motor stepping in the indicated direction with
every pulse applied to the step input.
/IP1/IP2BUSY
SERIAL OUT SERIAL IN
Vcc (+)GND (-)
COIL A COIL B COIL C COIL D CT - AC CT - BD
Vm (+)
A B C D Vom
L o g i c  S i g n a l s
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DC Characteristics
Characteristic Symbol Min Typ Max Unit Notes
Logic Supply Voltage V CC  4.5  5.0  5.5V
Vcc risetime t VCC0.05V/ms1
Logic supply current I CC  1.5  3.0mA
Input Low Voltage V IL0.0  1.0V
Input High Voltage V IH  4.3Vcc V
Output Low Voltage V OL0.6V
Output High Voltage V OH  4.3V
IP1/2 Source Current I OL  1.0mA
Motor Voltage V M50V
Motor current I M  3.0A
Motor resistance R M  2.8Ω
Clamp diode current I CL250mA
Step rate F STEP15000steps/sec
Speed Error F ERR+/- 0.5%2
Comms bit rate F BIT2400bps
BUSY rise/fall time T RF1025ns
Response time to IP1/2T INP1ms3
DIR hold time T DIR8us
Max Slave step rate F EXT10000steps/sec4
Operating temp t OP070°C5
Storage temp t ST-40100°C
[1]Required to ensure reliable startup.
[2]As a percentage of requested speed
[3]Response to IP is lesser of 1ms or 1 step
[4]If no comms while stepping. Max = 6000 steps/sec with comms
[5]Refer loading derating graph
Pin functions
Connector 1Pin Function
/IP1Optional input 1. Set home. Emergency stop.
/IP2Optional input 2. Set mark. Emergency stop.
BUSY Output - High when motor moving
SERIAL OUT Data from Little step-U to controller. TTL
SERIAL IN Data from controller to Little Step-U. TTL
Vcc Supply to logic circuits
GND Supply ground. Common with motor circuits.
Connector 2Pin Function
A Winding A output
B Winding B output
C Winding C output
D Winding D output
CT-AC Common for windings A & C
CT-BD Common for windings B & D
Connector 3Pin Function
V OM Motor supply ground. Common with logic circuits
V M Motor Supply +
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Hardware Connection
Power Supply
The Little Step-U divides the circuitry into two distinct sections with separate power supplies
required for the motor drive and the logic.  The logic/control section must be powered by a
regulated 5V supply applied to the VCC and GND pins.  The motor power supply voltage is
dictated by the motor characteristics and is connected to the VM(+) and VOM(-) pins.  The
GND and VOM pins are connected on the circuit board as a common reference.  The motor
power supply must have sufficient capacity for the motor and if the power supply is not
physically close to the motor/controller, a capacitor (eg. 4700uF) may be required at the
controller to ensure smooth operation of the motor.
Motor Connection
The motor connector has 4 connections (A, B, C & D) that are switched to ground in the
sequence required to cause the motor to step.  Note that stepper motor manufacturers have
several methods of labelling the connections to the motor.  The Little Step-U labels the pins in
the sequence they are switched when operating the motor with one coil on at a time and driving
in a clockwise direction. ie. A, then B, then C, then D and back to A.  The centre taps of the
two coils are connected to CT-AC and CT-BD, corresponding to the common connection of coils
A & C and coils
B & D respectively.  These two connections provide the freewheel diodes for
each of the motor coils and are connected on the circuit board.
IMPORTANT: A poor or intermittent connection to any of the stepper motor terminals can result
in destructive voltages being generated and causing permanent damage to the Little Step-U.
Similarly, do not connect or disconnect any stepper motor connections while power is applied.
The connection point between CT-AC and CT-BD is indicated on the circuit board by the
designator "LK".  This track can be cut and rejoined by soldering a wire between two pads if
needed.  In most cases this isn't required but is provided for applications using and L/xR
configuration in half step mode.
Interface connections
The Little Step-U acts on commands received serially from a host controller via the SERIAL IN
pin.  This is an asynchronous interface operating at 2400 bits per second, 8 data bits (LSB
first), 1 stop bit and no parity.  The signal levels are TTL.  Some commands illicit a response
and these are sent via the SERIAL OUT pin using the same protocol and signal levels as the
SERIAL IN pin.
When a command has been sent to the Little Step-U that causes the motor to move, the BUSY
pin will be high while the motor is in motion.
Two input pins are provided for use with stepper operation in the form of limit or home switches
or can be used as general inputs which can be read by software.  These pins accept logic level
inputs and will source 1mA when pulled low, making them suitable for direct connection to the
output of opto-couplers.
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Software commands
Communication with the Little Step-U is by a TTL level serial interface at 2400bps.  All
commands must begin with a "{" character and end with a "}"  Characters outside of the braces
(including carriage return and line feeds) are ignored.  Responses are enclosed by "[" and "]"
characters.
A - SET SPEED
Syntax{Axxxxx}Default value100 steps/sec
Sets the maximum speed in steps per second for any commands that follow.  The
numeric value can be any number from 1 to 5000.
B - SET RAMP TIME
Syntax{Bxxx}Default value0 seconds
The Little Step-U has a built in function to accelerate and decelerate the stepper motor
to/from the speed specified by the command above.  This command sets the amount of
time in tenths of a second that the motor will accelerate to that speed.  Valid numbers
are 0 to 200 being 0.0 to 20.0 seconds in 0.1 second increments.
Any move function that utilises the ramping facility will accelerate and decelerate at the
rate defined by this command.  The distance moved includes the steps used to ramp up
and ramp down so a move of 1000 steps will move exactly that amount.  If the number of
steps requested is less than the number required to ramp to full speed and ramp down
again, the Little Step-U will accelerate at the same rate until it is half way to its
destination and then ramp down again to stop at the commanded position.
See the discussion on ramping after the command descriptions.
C - SET STEP MODE
Syntax{Cx}Default value0 (Full step drive)
Stepper motors can be driven by powering the windings sequentially using three different
techniques.  The method used is specified by this command with x being 0, 1 or 2.
{C0}Full step
For every step, two windings are energised.
Step Coil A Coil B Coil C Coil D
1ON ON Off Off
2Off ON ON Off
3Off Off ON ON
4ON Off Off ON
controller翻译中文
{C1}Wave
Each step has only one winding energised.
Step Coil A Coil B Coil C Coil D
1ON Off Off Off
2Off ON Off Off
3Off Off ON Off
4Off Off Off ON
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{C2}Half step
Each alternate step has one or two windings energised giving the motor twice
the number of steps per revolution.
Step Coil A Coil B Coil C Coil D
1ON Off Off Off
2ON ON Off Off
3Off ON Off Off
4Off ON ON Off
5Off Off ON Off
6Off Off ON ON
7Off Off Off ON
8ON Off Off ON
When the mode is changed to or from Half step, the position, mark and speed values are
adjusted accordingly so that the motor will turn at the same rotational speed and the
mechanical positions remain unchanged.
Example:  A 200 step/rev motor is being used.  The current position is 3600, speed is set
at 200 steps per second and there is a mark at 1200.  When the mode is changed from
full-step to half step, the speed value will be 400 (giving the same number of revolutions of
the motor per second).  The current position register and the mark register will contain
the values 7200 and 2400 respectively.
D - GO TO ABSOLUT
E POSITION
Syntax{Dxxxxxxxx}
At anytime after powerup, the Little Step-U keeps track of its current position in steps.
This command instructs the Little Step-U to calculate the direction and number of steps
required to move to another position and then it performs the move.  At the end of the
move, the position will be the number specified in this command.  The value can be any
number from -10000000 to +10000000, including 0.  The number may be preceded by a
"+" or "-" as required, but must not include a comma or decimal point.
Example: If the current position is 2500, a command of {D-1000} will cause the motor to
run counter-clockwise for 1500 steps, stopping at position 1000.
E - GO TO RELATIVE POSITION
Syntax{Exxxxxx}
This command is similar to the "D" command in respect to the numeric parameter, but
commands the motor to move to a position relative to its current position.  Positive
numbers are clockwise and negative numbers are counter-clockwise.
Example: If the current position is 2500, a command of {E1000} will cause the motor to
run 1000 steps clockwise to end at position 3500.
F - GO TO ABSOLUTE POSITION WITH INPUTS 1 & 2 AS STOPS
Syntax{Fxxxxxx}
This command is the same as the "D" command except that the two input pins are
monitored.  If either of them is pulled low during the move, the motor will be decelerated
to a stop at the rate defined in the RAMP command (B).  The position register will reflect
the current position when the motor has stopped.  These inputs are level sensitive so if a
“F” command is used when one of the inputs is low, the motor will stop immediately.
Note:  Allowing the motor to continue to running past a stop indicator is done for two
reasons;  This method allows the motor to provide maximum braking torque during
deceleration and the position register integrity is maintained.
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Example: If the current position is 2500 and a limit switch attached to I/P2 is at position
5000, the command {F8000} will result in the motor stopping at position 5087 (depending
on the SPEED and RAMP settings).
G - GO TO RELATIVE POSITION WITH INPUTS 1 & 2 AS STOPS
Syntax{Gxxxxxx}
This command is the same as the "E" command except that the two input pins are
monitored as in the command above.
Example: If the current position is 2500 and a limit switch attached to I/P1 is at the home
position (0), the command {G-5000} will result in the motor stopping at position -87
(depending on the SPEED and RAMP settings).
H - GO CLOCKWISE UNTIL INPUT 2
Syntax{H}
This command is used to find a limit stop connected to I/P2 and has no numeric
parameter.  The motor will accelerate at the rate determined by the RAMP setting, up to
the SPEED setting and not stop (ramp down) until I/P2 is pulled low.
Example: The motor is at position 28 and a limit switch is at position 1000.  The SPEED
has been set to a slow value and RAMP set to 0.  After an {H} command the position is
1000.
J - GO COUNTER-CLOCKWISE UNTIL INPUT 1 AND ZERO POSITION
Syntax{J}
The J command is similar to the H command above except that the direction is reversed
and I/P1 is used to halt the movement.  When the movement is stopped, the position
register is cleared to 0 to mark this position as "Home".
Example: The motor is at an unknown position and a {J} command is used at a slow
speed and 0 RAMP rate.  At the end of the movement (dictated by I/P1) the position
register is 0.
K - GO CLOCKWISE UNTIL INPUT 2 AND MARK POSITION
Syntax{K}
The motor runs continuously in a clockwise direction until stopped by I/P2 being pulled
low.  When this occurs, the position is recorded in the MARK register.
Example: The motor has been moved to the home position using the {J} command.
Issuing a {K} command will run the motor and when it has stopped, the position of the
other limit switch has been recorded.
M - GO TO THE MARK POSITION
Syntax{M}
This command instructs the Little Step-U to move to the absolute position held in the
"Mark" register.  The contents of this register is set to 0 when the device is powered on
and can be set using the "K" or "R" commands.  As with the "D" (Go to absolute
position) command, the controller will determine the direction and will use the Ramp and
Speed settings to move to that position.
Example: The Little Step-U is being used in a component placement machine and the
position to pick up the next component is known to always be 123456.  After each
placement, a {M} command will place the pickup head over the next component to be
placed.
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