L6208Q View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6208Q' PDF : 34 Pages View PDF
L6208Q
Circuit description
5.5
Stepping sequence generation
The phase sequence generator is a state machine that provides the phase and enable
inputs for the two bridges to drive a stepper motor in either full step or half step. Two full step
modes are possible, the normal drive mode where both phases are energized at each step
and the wave drive mode where only one phase is energized at a time. The drive mode is
selected by the HALF/FULL input and the current state of the sequence generator, as
described below. A rising edge of the CLOCK input advances the state machine to the next
state. The direction of rotation is set by the CW/CCW input. The RESET input resets the
state machine to state.
5.6
Half step mode
A HIGH logic level on the HALF/FULL input selects half step mode. Figure 18 shows the
motor current waveforms and the state diagram for the phase sequencer generator. At
startup or after a RESET the phase sequencer is at state 1. After each clock pulse the state
changes following the sequence 1, 2, 3, 4, 5, 6, 7, 8, etc. if CW/CCW is high (clockwise
movement) or 1, 8, 7, 6, 5, 4, 3, 2, etc. if CW/CCW is low (counterclockwise movement).
5.7
Normal drive mode (full step two-phase-on)
A low level on the HALF/FULL input selects the full step mode. When the low level is
applied, when the state machine is at an ODD numbered state, normal drive mode is
selected. Figure 19 shows the motor current waveform state diagram for the state machine
of the phase sequencer generator. Normal drive mode can easily be selected by holding the
HALF/FULL input low and applying a RESET. At startup or after a RESET the state machine
is in state 1. While, when the HALF/FULL input is kept low, the state changes following the
sequence 1, 3, 5, 7, etc. if CW/CCW is high (clockwise movement) or 1, 7, 5, 3, etc. if
CW/CCW is low (counterclockwise movement).
5.8
Wave drive mode (full step one-phase-on)
A low level on the pin HALF/FULL input selects the full step mode. When the low level is
applied, when the state machine is at an EVEN numbered state, the wave drive mode is
selected. Figure 20 shows the motor current waveform and the state diagram for the state
machine of the phase sequence generator. To enter wave drive mode the state machine
must be in an EVEN numbered state. The most direct method to select the wave drive mode
is to first apply a RESET, then while keeping the HALF/FULL input high, apply one pulse to
the clock input, then take the HALF/FULL input low. This sequence first forces the state
machine to state 1. The clock pulse, with the HALF/FULL input high, advances the state
machine from state 1 to either state 2 or 8 depending on the CW/CCW input. Starting from
this point, each clock pulse (rising edge) advances the state machine following the
sequence 2, 4, 6, 8, etc. if CW/CCW is high (clockwise movement) or 8, 6, 4, 2, etc.
if CW/ CCW is low (counterclockwise movement).
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