LM628 datasheet(16/24 Pages) NSC

16 / 24 page

Trajectory Control Commands

(Continued)

the current user-programmed acceleration value. Bits 8

through 10 are to be used

exclusively; only one bit should be

a logic one at any time.

Bits 0 through 5 inform the LM628 as to whether any or all of

the trajectory controlling parameters are about to be written,

and whether the data should be interpreted as absolute or

relative. The user may choose to update any or all (or none)

of the trajectory parameters. Those chosen for updating are

so indicated by logic one(s) in the corresponding bit posi-

tion(s). Any parameter may be changed while the motor is in

motion; however, if acceleration is changed then the next

STT command must not be issued until the LM628 has com-

pleted the current move or has been manually stopped.

The data bytes specified by and immediately following the

trajectory control word are written in pairs which comprise

16-bit words. Each data item (parameter) requires two 16-bit

words; the word and byte order is most-to-least significant.

The order of sending the parameters to the LM628 corre-

sponds to the descending order shown in the above descrip-

tion of the trajectory control word; i.e., beginning with accel-

eration, then velocity, and finally position.

Acceleration and velocity are 32 bits, positive only, but range

only from 0 (00000000 hex) to [2

30]−1 (3FFFFFFF hex). The

bottom 16 bits of both acceleration and velocity are scaled

as fractional data; therefore, the least-significant integer data

bit for these parameters is bit 16 (where the bits are num-

bered 0 through 31). To determine the coding for a given ve-

locity, for example, one multiplies the desired velocity (in

counts per sample interval) times 65,536 and converts the

result to binary. The units of acceleration are counts per

sample per sample. The value loaded for acceleration must

not exceed the value loaded for velocity. Position is a signed,

32-bit integer, but ranges only from −[2

30] (C0000000 hex) to

30]−1 (3FFFFFFF Hex).

The required data is written to the primary buffers of a

double-buffered scheme by the above described operations;

it is not transferred to the secondary (working) registers until

the STT command is executed. This fact can be used advan-

tageously; the user can input numerous data ahead of their

actual use. This simple pipeline effect can relieve potential

host computer data communications bottlenecks, and facili-

tates easier synchronization of multiple-axis controls.

STT COMMAND: STarT Motion Control

Command Code:

01 Hex

Data Bytes:

None

Executable During Motion: Yes, if acceleration has not

been changed

The STT command is used to execute the desired trajectory,

the specifics of which have been programmed via the LTRJ

command. Synchronization of multi-axis control (to within

one sample interval) can be arranged by loading the re-

quired trajectory parameters for each (and every) axis and

then simultaneously issuing a single STT command to all

axes. This command may be executed at any time, unless

the acceleration value has been changed and a trajectory

has not been completed or the motor has not been manually

stopped. If STT is issued during motion and acceleration has

been changed, a command error interrupt will be generated

and the command will be ignored.

Data Reporting Commands

The following seven LM628 user commands are used to ob-

tain data from various registers in the LM628. Status, posi-

tion, and velocity information are reported. With the excep-

tion of RDSTAT, the data is read from the LM628 data port

after first writing the corresponding command to the com-

mand port.

RDSTAT COMMAND: ReaD STATus Byte

Command Code:

None

Byte Read:

One

Data Range:

See Text

Executable During Motion: Yes

The RDSTAT command is really not a command, but is listed

with the other commands because it is used very frequently

to control communications with the host computer. There is

no identification code; it is directly supported by the hard-

ware and may be executed at any time. The single-byte sta-

tus read is selected by placing CS , PS and RD at logic zero.

See

Table 7.

TABLE 7. Status Byte Bit Allocation

Bit Position

Function

Bit 7

Motor Off

Bit 6

Breakpoint Reached [Interrupt]

Bit 5

Excessive Position Error [Interrupt]

Bit 4

Wraparound Occurred [Interrupt]

Bit 3

Index Pulse Observed [Interrupt]

Bit 2

Trajectory Complete [Interrupt]

Bit 1

Command Error [Interrupt]

Bit 0

Busy Bit

Bit 7, the motor-off flag, is set to logic one when the motor

drive output is off (at the half-scale, offset-binary code for

zero). The motor is turned off by any of the following condi-

tions: power-up reset, command RESET, excessive position

error (if command LPES had been executed), or when com-

mand LTRJ is used to manually stop the motor via turning

the motor off. Note that when bit 7 is set in conjunction with

command LTRJ for producing a manual, motor-off stop, the

actual setting of bit 7 does not occur until command STT is

issued to affect the stop. Bit 7 is cleared by command STT,

except as described in the previous sentence.

Bit 6, the breakpoint-reached interrupt flag, is set to logic one

when the position breakpoint loaded via command SBPA or

SBPR has been exceeded. The flag is functional indepen-

dent of the host interrupt mask status. Bit 6 is cleared via

command RSTI.

Bit 5, the excessive-position-error interrupt flag, is set to

logic one when a position-error interrupt condition exists.

This occurs when the error threshold loaded via command

LPEI or LPES has been exceeded. The flag is functional in-

dependent of the host interrupt mask status. Bit 5 is cleared

via command RSTI.

Bit 4, the wraparound interrupt flag, is set to logic one when

a numerical “wraparound” has occurred. To “wraparound”

means to exceed the position address space of the LM628,

which could occur during velocity mode operation. If a wrap-

around has occurred, then position information will be in er-

ror and this interrupt helps the user to ensure position data

integrity. The flag is functional independent of the host inter-

rupt mask status. Bit 4 is cleared via command RSTI.

LM628 Datasheet(PDF) 16 Page - National Semiconductor (TI)

LM628 Datasheet(HTML) 16 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL