L6208PD datasheet(19/35 Pages) STMICROELECTRONICS

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L6208

Decay modes

7.1

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 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.

7.2

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).

7.3

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 the normal drive mode is

selected. Figure 19 shows the motor current waveform state diagram for the state machine

of the phase sequencer generator. The 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 the HALF/FULL input is kept low, 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).

7.4

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 the 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, after each clock pulse (rising edge) will advance 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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