Executable During Motion: Yes

The UDF command is used to update the filter parameters,

the specifics of which have been programmed via the LFIL

command. Any or all parameters (derivative-term sampling

interval, kp, ki, kd, and/or il) may be changed by the appro-

priate command(s), but command UDF must be executed to

affect the change in filter tuning. Filter updating is synchro-

nized with the calculations to eliminate erratic or spurious

behavior.

Trajectory Control Commands

The following two LM628 user commands are used for set-

ting the trajectory control parameters (position, velocity, ac-

celeration), mode of operation (position or velocity), and di-

rection (velocity mode only) as required to describe a

desired motion or to select the mode of a manually directed

stop, and to control the timing of these system changes.

LTRJ COMMAND: Load TRaJectory Parameters

Command Code:

1F Hex

Data Bytes:

Two to Fourteen

Data Ranges…

Trajectory Control

Word:

See Text

Position:

C0000000 to 3FFFFFFF Hex

Velocity:

00000000 to 3FFFFFFF Hex

(Pos Only)

Acceleration:

00000000 to 3FFFFFFF Hex

(Pos Only)

Executable During

Motion:

Conditionally, See Text

TABLE 5. Derivative-Term Sampling Interval Selection Codes

Bit Position

Selected Derivative

15

14

13

12

11

10

9

8

Sampling Interval

000000

0

0

256 µs

000000

0

1

512 µs

000000

1

0

768 µs

000000

1

1

1024 µs, etc…

thru

111111

1

1

65,536 µs

Note 8: Sampling intervals shown are when using an 8.0 MHz clock. The 256 corresponds to 2048/8 MHz; sample intervals must be scaled for other clock frequen-

cies.

The trajectory control parameters which are written to the

LM628 to control motion are: acceleration, velocity, and po-

sition. In addition, indications as to whether these three pa-

rameters are to be considered as absolute or relative inputs,

selection of velocity mode and direction, and manual stop-

ping mode selection and execution are programmable via

this command. After writing the command code, the first two

data bytes that are written specify which parameter(s) is/are

being changed. The first byte written is the more significant.

Thus the two data bytes constitute a trajectory control word

that informs the LM628 as to the nature and number of any

following data bytes. See

Table 6.

TABLE 6. Trajectory Control Word Bit Allocation

Bit Position

Function

Bit 15

Not Used

Bit 14

Not Used

Bit 13

Not Used

Bit 12

Forward Direction (Velocity Mode Only)

Bit 11

Velocity Mode

Bit 10

Stop Smoothly (Decelerate as

Programmed)

Bit 9

Stop Abruptly (Maximum Deceleration)

Bit 8

Turn Off Motor (Output Zero Drive)

Bit 7

Not Used

Bit 6

Not Used

Bit Position

Function

Bit 5

Acceleration Will Be Loaded

Bit 4

Acceleration Data Is Relative

Bit 3

Velocity Will Be Loaded

Bit 2

Velocity Data Is Relative

Bit 1

Position Will Be Loaded

Bit 0

Position Data Is Relative

Bit 12 determines the motor direction when in the velocity

mode. A logic one indicates forward direction. This bit has no

effect when in position mode.

Bit 11 determines whether the LM628 operates in velocity

mode (Bit 11 logic one) or position mode (Bit 11 logic zero).

Bits 8 through 10 are used to select the method of

manually

stopping the motor. These bits are not provided for one to

merely specify the desired

mode of stopping, in position

mode operations, normal stopping is always smooth and oc-

curs automatically at the end of the specified trajectory. Un-

der exceptional circumstances it may be desired to manually

intervene with the trajectory generation process to affect a

premature stop. In velocity mode operations, however, the

normal means of stopping

is via bits 8 through 10 (usually bit

10). Bit 8 is set to logic one to stop the motor by turning off

motor drive output (outputting the appropriate offset-binary

code to apply zero drive to the motor); bit 9 is set to one to

stop the motor abruptly (at maximum available acceleration,

by setting the target position equal to the current position);

and bit 10 is set to one to stop the motor smoothly by using

www.national.com

15