LM628, LM629

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SNVS781C – JUNE 1999 – REVISED MARCH 2013

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 required 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 obtain data from various registers in the LM628. Status,

position, and velocity information are reported. With the exception of RDSTAT, the data is read from the LM628

data port after first writing the corresponding command to the command 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 hardware and may be executed at any time. The single-byte status 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 conditions: power-up reset, command RESET, excessive

position error (if command LPES had been executed), or when command 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 independent 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 independent 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 wraparound has occurred, then position information will be in error and this interrupt helps

the user to ensure position data integrity. The flag is functional independent of the host interrupt mask status. Bit

4 is cleared via command RSTI.

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