9

Micr ostep Select

(MSEL) Inputs

The Microstep Select inputs are used to

select the number of fractional steps per full

step that the IM2000S will output to the

motor. These inputs are buffered using

Schmitt trigger buffers to increase noise

immunity. There are 14 different selections

built into the IM2000S. Table 3.1 shows the

list of resolutions and their relationship to

the state of the MSEL inputs.

A unique feature of the IM2000S is the

ability to change resolutions at any time. A

resolution change can occur whether the

motor is being clocked or is at rest. The

change will not take place until the rising

edge of the next step clock input. At this

time, the new resolution is latched and

implemented before the step clock pulse

takes affect.

If a resolution is chosen such that the sine/

cosine output of the IM2000S would not

land on an electrical fullstep of the motor,

then the IM2000S will automatically align

itself to the full step position on the step

clock pulse that would have caused the motor

to rotate past the full step. The step clock pulses, from that point forward will be equal to the selected resolution. This

feature allows the user to switch resolutions at any time without having to keep track of sine/cosine location. The user

can now easily track position utilizing the full step output signal.

The capability of changing resolutions on-the-fly allows for high speed slewing where bandwidth is limited, as is the case

with many single chip microcontrollers. The user may switch to a coarser resolution during long moves for increased

speed, then change to a finer resolution for precise positioning at the end of travel.

Step/Dir ection Inputs

The IM2000S contains a built-in sine/cosine generator used for the generation of Phase A and Phase B position

reference. This digitally encoded 9 bit sine and 9 bit cosine signal is directly fed into a digital-to-analog converter.

The step clock (SCLK) and direction (DIR) inputs are buffered using Schmidt triggered buffers for increased noise

immunity and are used to increment or decrement the sine/cosine position generator. The position generator is updated

on the rising edge of the step clock input. It will increment or decrement by the amount specified by the microstep

resolution select (MSEL) inputs.

The direction (DIR) input determines the direction of the position generator and hence the direction of the motor. The

DIR input is synchronized to the SCLK input. On the rising edge of the SCLK input, the state of the DIR input is

latched in. The position generator will then look to see if there has been a change in direction and implement that

change before executing the next step. By utilizing this method to implement the direction change, the noise immunity

is greatly increased and no physical change in the motor occurs if the direction line is toggled prior to the step clock

input.

The enable/disable input does not affect the step clock input. The sine/cosine generator will continue to update if a signal

is applied to the step clock input. The IM2000S outputs both sine and cosine data simultaneously when applying a step

clock input. Dual internal look-up tables are used to output a unique position for every step clock input to enhance

system performance.

Truth Table: Resolution Select Inputs -Binary Mode

Truth Table: Resolution Select Inputs - Decimal Mode

Invalid Microstep Resolution Settings

Table 3.1: Microstep Resolution Settings

p

e

t

S

l

l

u

F

r

e

p

s

p

e

t

s

o

r

c

i

M

3

L

E

S

M

2

L

E

S

M

1

L

E

S

M

0

L

E

S

M

2

0000

4

0

0

0

1

80

0

1

0

6

1

0

0

1

1

2

30

1

0

0

4

6

0

1

0

1

8

2

10

1

1

0

6

5

2

0

1

1

1

p

e

t

S

l

l

u

F

r

e

p

s

p

e

t

s

o

r

c

i

M

3

L

E

S

M

2

L

E

S

M

1

L

E

S

M

0

L

E

S

M

5

1

000

0

1

1

0

0

1

5

21

0

1

0

0

5

1

0

1

1

5

2

11

1

0

0

0

5

2

1

1

0

1

p

e

t

S

l

l

u

F

r

e

p

s

p

e

t

s

o

r

c

i

M

3

L

E

S

M

2

L

E

S

M

1

L

E

S

M

0

L

E

S

M

X

X

X

X

X

X

X

111

0

X

X

X

X

X

X

X

1

1

1

1