Instruction LPES is essentially the same as command LPEI
above, but adds the feature of turning off the motor upon de-
tecting excessive position error. The motor drive is not actu-
ally switched off, it is set to half-scale, the offset-binary code
for zero. As with command LPEI, bit 5 of the status byte is
also set to logic high. The first byte of threshold data written
with command LPES is the more significant. The user can
have the LM628 interrupt the host to signify that an exces-
sive position error has occurred. See the descriptions for
commands MSKI and RSTI.
Initialization Commands (Continued)
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 com-
puter. 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).
SBPA COMMAND:
Command Code:
Data Bytes:
20 Hex
Four
Data Range:
C0000000 to 3FFFFFFF Hex
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 poll-
ing the LM628 for status information, as opposed to interrupt
driven operation.
Executable During Motion: Yes
This command enables the user to set a breakpoint in terms
of absolute position. Bit 6 of the status byte is set to logic
high when the breakpoint position is reached. This condition
is useful for signaling trajectory and/or filter parameter up-
dates. The user can also arrange to have the LM628 inter-
rupt the host to signify that a breakpoint position has been
reached. See the descriptions for commands MSKI and
RSTI.
SIP COMMAND: Set Index Position
Command Code:
Data Bytes:
03 Hex
None
Executable During Motion: Yes
SBPR COMMAND:
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 de-
scription for command RDIP) to facilitate aligning the defini-
tion 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.
Command Code:
Data Bytes:
21 Hex
Four
Data Range:
See Text
Executable During Motion: Yes
This command enables the user to set a breakpoint in terms
of relative position. As with command SBPA, bit 6 of the sta-
tus byte is set to logic high when the breakpoint position
(relative to the current commanded target position) is
reached. The relative breakpoint input value must be such
that when this value is added to the target position the result
remains within the absolute position range of the system
(C0000000 to 3FFFFFFF hex). This condition is useful for
signaling trajectory and/or filter parameter updates. The user
can also arrange to have the LM628 interrupt the host to sig-
nify that a breakpoint position has been reached. See the de-
scriptions for commands MSKI and RSTI.
LPEI COMMAND: Load Position Error for Interrupt
Command Code:
Data Bytes:
1B Hex
Two
Data Range:
0000 to 7FFF Hex
Executable During Motion: Yes
MSKI COMMAND: MaSK Interrupts
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 mo-
tor 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 po-
sition error has occurred. See the descriptions for com-
mands MSKI and RSTI.
Command Code:
Data Bytes:
1C Hex
Two
Data Range:
See Text
Executable During Motion: Yes
The MSKI command lets the user determine which potential
interrupt condition(s) will interrupt the host. Bits 1 through 6
of the status byte are indicators of the six conditions which
are candidates for host interrupt(s). When interrupted, the
host then reads the status byte to learn which condition(s)
occurred. Note that the MSKI command is immediately fol-
lowed by two data bytes. Bits 1 through 6 of the second (less
significant) byte written determine the masked/unmasked
status of each potential interrupt. Any zero(s) in this 6-bit
field will mask the corresponding interrupt(s); any one(s) en-
able the interrupt(s). Other bits comprising the two bytes
have no effect. The mask controls only the host interrupt pro-
cess; reading the status byte will still reflect the actual condi-
tions independent of the mask byte. See Table 3.
LPES COMMAND: Load Position Error for Stopping
Command Code:
Data Bytes:
1A Hex
Two
Data Range:
0000 to 7FFF Hex
Executable During Motion: Yes
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