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MicrostepPLD Driver Manual





MicrostepPLD Driver Manual
Version 6/13/2006






















Embedded Acquisition Systems
2517 Cobden Street
Sterling Heights, MI
48310
http://www.embeddedtronics.com
email sales@embeddedtronics.com
copyright 2003-2004
EAS MicrostepPLD is our 2 axis microstepping chopper driver board for stepper
motors. It is based on the National Semiconductor LMD18245 3amp 55volt full
bridge motor driver.

Specifications:
Xilinx CPLD based.
2 axis driver on one single board.
Supports half/full steps plus 4,5,6,8,10, or 16 microstep modes. Only one stepper
mode can be programmed into the CPLD at one time, please state which version
required when ordering.
Drives 4,6 or 8 wire bipolar/ unipolar stepper motors up to 3amps at 55volts per
phase.
Adjustable chopper current drive.
Standard TTL step, direction and enable inputs.

Power connections.
The EAS MicrostepPLD driver board has a 55Volt maximum input voltage for
powering stepper motors. Power leads must be connected to correct terminal
screw. Do not reverse the power input or exceed 55volts, the LMD18245 drivers
can be damaged by this.

Connect your stepper power supply to the MOT PWR screw terminal located on
the right side of the board. Positive supply input connects to screw terminal
labeled +.

If stepper motor power supply is far away from driver board, connect a 470uf
65volt capacitor directly to MOT PWR screw terminals.

The driver board also requires a separate supply to power the low voltage
section of the driver board. Connect an 8-12volt supply to the screw terminals
labeled PWR and GND. The PWR terminal is +positive supply input. This
terminal is located near the front right side of the board. You can use the 12volt
computer disk drive cable connector to supply power to the board. This is the
recommended way to hook up power to the onboard 5 volt regulator.

Always turn on the low voltage power supply/Computer before turning on the
higher voltage stepper motor power supply.

Motor Power Supply
A standard 24volt AC transformer works well. This is approximately 35volts DC
after diodes and filtering caps are added to complete the power supply. We
recommend using an unregulated linear power supply and not a switching type
supply. If using a switching type supply, place a large capacitor (10,000uf or
more) on the output terminals. A 3amp/phase stepper motor will only require a
2amp power supply. For multiple stepper motors, add up all the current/phase
required and multiply by 2/3 to calculate the minimum power supply current rating needed. Do not connect or disconnect any stepper motor leads while motor
supply is connected and turned on. This may damage the LMD18245 driver
chips.

The LMD18245 driver chip is rated at 55volts maximum DC input. When using a
power supply that is over 45volts, there will be some motor back EMF, induced
by stepper motor deceleration, which may cause the voltage to rise above the
rated 55volt limit. For added protection, place a correctly rated zener diode to
help clamp the voltage below 55volts. We also recommend placing a fast blow
5amp fuse on the motor supply input connector for each driver board.

Step/Direction connections.
If you are using the parallel port Breakout Board, connect the step, direction and
ground terminals to the corresponding screw terminals on the MicrostepPLD
driver board. ST1/DR1 terminals are the step and direction inputs to the
LMD18245 A and B stepper motor driver. ST2/DR2 terminals are the step and
direction inputs to the LMD18245 C and D stepper motor driver.

If the Breakout Board isnt used, you will need to connect the appropriate step
and direction I/O pins from the PC parallel port to the MicrostepPLD driver board.
You will also need to connect the parallel port ground, pin 25, to the terminal
labeled GND on the driver board. Please read the TurboCNC or MACH2 manual
for more info on correct step and direction pin I/O assignments.

The step and direction signals should be set to Active Low pin state with a
pulse width atleast 1 microseconds. Some external parallel port optoisolation
boards invert the step and direction signals. If this is the case, set the pin state to
Active High.

Enable Connection
EN1 and EN2 terminals can be used to disable power to the stepper motors. A
low signal will disable and will stop the stepper motors.

EN1 terminal is used to disable the LMD18245 A and B stepper motor drivers.
EN2 terminal is used to disable the LMD18245 C and D stepper motor drivers.

Normal operation, the enable terminals is high or set to +5 volts. If this feature
isnt needed, you can connect EN1 and EN2 to the terminal labeled VCC with a
short piece of wire. VCC is +5 output from the onboard voltage regulator.

Current Resistor Setting
The maximum driver current output is set by resistor R6/R14 and R7/R15. The
LMD18245 can drive stepper motors up to 3amps per phase. Higher current
rated stepper motors can be used but maximum listed torque will not be
achieved. You must attach the LMD18245 driver chips to a large heatsink for
them to operate properly. There is a small hole on each tab for a screw to help mount them to a heatsink securely. Use white silicon heatsink compound for
better heat transfer. The tabs on the LMD18245 is the same as ground, do not
let bare wires touch the heatsink or driver chips. A fan blowing directly on the
heatsink is also highly recommended.

The current sense resistor can be calculated by the following formula:

18,750 / A = R

R value is in ohms
A value is in amps

Current resistor typical values:
R=18.75K 1amp
R=9.38K 2amp
R=7.5K 2.5amp
R=6.25K 3amp
Use 1/4 watt resistors and do not use lower than a 6.25K value.

Each pair of LMD18245 driver chips must be set to the same output current limit.
Use the same resistor value for R6 and R14 for drivers A and B. Also the same
resistor value for R7 and R15 for drivers C and D. Do not set the drivers to output
more than 3 amps, they will fail. If you have two stepper motors with different
current ratings, drivers A and B can be set to different current output rating than
drivers C and D.

Optional variable current output can be had by removing resistor R6,R14,R7,R15
and installing the 25K pots R8,R16,R9,R17 and 6.25K resisters R4,R12,R5,R13.
The set resistance value must not be lower than 6.25K. We recommend users to
install resisters R6,R14,R7,R15 instead of the variable pots.

J3 Ground solder point.
You must solder together jumper J3 on the driver board or the board will not
function. This connects the analog ground to the digital ground. It is located in
near the right side of the board, silkscreened labeled SHORT.

Future upgrade.
When we designed this board, we put in some additional parts on the schematic
for future expansion capability. The parts listed on the schematic lower left hand
can be ignored.

Do not install:
U7 oscillator
U8 reset chip
Headers JP8, JP10 and JP2
Resisters R19,20,21,22 Stepper motor driver connections.

4 wire stepper motor connection.

For stepper motor 1
Wire 1 connects to A1 terminal
Wire 2 connects to A2 terminal
Wire 3 connects to B1 terminal
Wire 4 connects to B2 terminal

For stepper motor 2
Wire 1 connects to C1 terminal
Wire 2 connects to C2 terminal
Wire 3 connects to D1 terminal
Wire 4 connects to D2 terminal

Adjust drive current setting to no more than motor rated current specification.

1
2
4
3


















6 wire stepper motor, half winding connection.

For stepper motor 1
Wire 1 connects to A1 terminal
Wire 2 connects to A2 terminal
Wire 3 not connected
Wire 4 connects to B1 terminal
Wire 5 connects to B2 terminal
Wire 6 not connected

For stepper motor 2
Wire 1 connects to C1 terminal
Wire 2 connects to C2 terminal
Wire 3 not connected
Wire 4 connects to D1 terminal
Wire 5 connects to D2 terminal
Wire 6 not connected

Adjust drive current setting to no more than motor rated current specification.

This is the preferable way to hook up a 6 wire stepper motor to the driver. 6 wire
half winding mode has lower inductance than 6 wire full winding. The stepper
motor will be able to spin faster.

1
2
3
4
5
6












6 wire stepper motor, full winding connection.

For stepper motor 1
Wire 1 connects to A1 terminal
Wire 2 not connected
Wire 3 connects to A2 terminal
Wire 4 connects to B1 terminal
Wire 5 not connected
Wire 6 connects to B2 terminal

For stepper motor 2
Wire 1 connects to C1 terminal
Wire 2 not connected
Wire 3 connects to C2 terminal
Wire 4 connects to D1 terminal
Wire 5 not connected
Wire 6