POWERSTEP01 datasheet(53/92 Pages) STMICROELECTRONICS

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powerSTEP01

Programming manual

11.1.1

ABS_POS

The ABS_POS register contains the current motor absolute position in agreement with the

selected step mode; the stored value unit is equal to the selected step mode (full, half,

quarter, etc.). The value is in 2 's complement format and it ranges from -221 to +221-1.

At power-on the register is initialized to “0” (HOME position).

Any attempt to write the register when the motor is running causes the command to be

ignored and the CMD_ERROR flag to rise (Section 11.1.28 on page 71).

11.1.2

EL_POS

The EL_POS register contains the current electrical position of the motor. The two MSbits

indicate the current step and the other bits indicate the current microstep (expressed in

step/128) within the step.

When the EL_POS register is written by the user the new electrical position is instantly

imposed. When the EL_POS register is written, its value must be masked in order to match

with the step mode selected in the STEP_MODE register in order to avoid a wrong

microstep value generation (Section 11.1.23 on page 61); otherwise the resulting microstep

sequence is incorrect. When the device operates in current mode, the bit number 0, 1 and 2

of the EL_POS register are meaningless because the maximum microstepping resolution is

1/16th of step.

Any attempt to write the register when the motor is running causes the command to be

ignored and the CMD_ERROR flag to rise (Section 11.1.28).

11.1.3

MARK

The MARK register contains an absolute position called MARK, according to the selected

step mode; the stored value unit is equal to the selected step mode (full, half, quarter, etc.).

It is in 2's complement format and it ranges from -221 to +221-1.

11.1.4

SPEED

The SPEED register contains the current motor speed, expressed in step/tick (format

unsigned fixed point 0.28).

In order to convert the SPEED value in step/s the following formula can be used:

Equation 4

where SPEED is the integer number stored in the register and tick is 250 ns.

The available range is from 0 to 15625 step/s with a resolution of 0.015 step/s.

Note:

The range effectively available to the user is limited by the MAX_SPEED parameter.

Table 13. EL_POS register

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

STEP

MICROSTEP

step/s

 SPEED 2

–



tick

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