ELM311
Pin Descriptions
VDD (pin 1)
Step (pin 4)
This pin is the positive supply pin, and should
always be the most positive point in the circuit.
Internal circuitry connected to this pin is used to
provide power on reset of the microprocessor, so
an external reset signal is not required. Refer to
the Electrical Characteristics section for further
information.
This input is used to control the motion of the
motor. Outputs will change to their next state on
the high to low transition of this input. Step is
normally maintained at a low level, and is only
brought high then low to cause a step to occur.
The Step input is ignored for about 20ms after
power-up to allow sufficient time for external
circuits to stabilize.
A (pin 2)
D (pin 5)
This is the active high output drive signal for the
(first) phase A winding. Normally, this output
would be the first to be energized when starting a
stepping sequence, and is always the first state
entered into internally on powerup. After powerup,
however, the ELM311 treats this pin specially,
maintaining it at a low level until the first step
command is received. This in effect keeps the
motor off until selected by control circuitry.
This is the active high output drive signal for the
(fourth) phase D winding.
C (pin 6)
This is the active high output drive signal for the
(third) phase C winding.
B (pin 7)
This is the active high output drive signal for the
(second) phase B winding.
Dir (pin 3)
This pin determines the sequence that the outputs
will be energized in. A high input on the Dir pin
while the step input is pulsed will cause a single
clockwise step, while a low level will cause a
counter-clockwise step. (See Figure 1 on page 4)
VSS (pin 8)
Circuit common is connected to this pin. This is
the most negative point in the circuit.
Dir must be at a stable level prior to the low to
high transition of Step in order to be recognized
(refer to the Tsu specification).
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface
mount type of package. To order, add the appropriate suffix to the part number:
300 mil Plastic DIP............................... ELM311P
200 mil SOIC..................................... ELM311SM
All rights reserved. Copyright ©1999 Elm Electronics.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
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ELM311DSB
Elm Electronics – Circuits for the Hobbyist
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