LM628, LM629

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SNVS781C – JUNE 1999 – REVISED MARCH 2013

DFH COMMAND: DEFINE HOME

Command Code: 02 Hex

Data Bytes: None

Executable During Motion: Yes

This command declares the current position as “home”, or absolute position 0 (Zero). If DFH is executed during

motion it will not affect the stopping position of the on-going move unless command STT is also executed.

Interrupt Control Commands

The following seven LM628 user commands are associated with conditions which can be used to interrupt the

host computer. In order for any of the potential interrupt conditions to actually interrupt the host via Pin 17, the

corresponding bit in the interrupt mask data associated with command MSKI must have been set to logic high

(the non-masked state).

The identity of all interrupts is made known to the host via reading and parsing the status byte. Even if all

interrupts are masked off via command MSKI, the state of each condition is still reflected in the status byte. This

feature facilitates polling the LM628 for status information, as opposed to interrupt driven operation.

SIP COMMAND: SET INDEX POSITION

Command Code: 03 Hex

Data Bytes: None

Executable During Motion: Yes

After this command is executed, the absolute position which corresponds to the occurrence of the next index

pulse input will be recorded in the index register, and bit 3 of the status byte will be set to logic high. The position

is recorded when both encoder-phase inputs and the index pulse input are logic low. This register can then be

read by the user (see description for command RDIP) to facilitate aligning the definition of home position (see

description of command DFH) with an index pulse. The user can also arrange to have the LM628 interrupt the

host to signify that an index pulse has occurred. See the descriptions for commands MSKI and RSTI.

LPEI COMMAND: LOAD POSITION ERROR FOR INTERRUPT

Command Code: 1B Hex

Data Bytes: Two

Data Range: 0000 to 7FFF Hex

Executable During Motion: Yes

An excessive position error (the output of the loop summing junction) can indicate a serious system problem;

e.g., a stalled rotor. Instruction LPEI allows the user to input a threshold for position error detection. Error

detection occurs when the absolute magnitude of the position error exceeds the threshold, which results in bit 5

of the status byte being set to logic high. If it is desired to also stop (turn off) the motor upon detecting excessive

position error, see command LPES, below. The first byte of threshold data written with command LPEI is the

more significant. The user can have the LM628 interrupt the host to signify that an excessive position error has

occurred. See the descriptions for commands MSKI and RSTI.

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Product Folder Links: LM628 LM629