MC1151A PMD, MC1151A Datasheet - Page 23

• Manufacturer Part Number: MC1151A
• Description: (MC1x51A) Advanced Step Motor Control Chipset
• Manufacturer: PMD

consists of a bit mask, with 1 bit assigned to each axis. Executing this
command has the same affect as instantaneously switching to each
desired axes, and executing an UPDATE command.
Breakpoints
A breakpoint is a convenient way of programming a profile or other
double-buffered parameter change upon some specific condition. There
are two types of breakpoints, those that have a 32-bit comparitor value
associated with them and those that do not. For those that have the
comparitor, a 32-bit comparitor value is loaded into the breakpoint
compare register first, and then one of the breakpoint conditions is
specified. For those breakpoint modes without associated comparitor
values only the breakpoint condition needs to be specified.
The double-buffered registers and commands will be updated upon
satisfaction of the specified breakpoint condition.
Here is a list of all of the available breakpoint conditions.
Positive Target Position Breakpoint
Negative Target Position Breakpoint
Positive Actual Position Breakpoint
Negative Actual Position Breakpoint
Time Breakpoint
A 32 bit position breakpoint can be specified which will result in
the parameters being updated when the current target position
(the instantaneous desired axis position output from the profile
generator) equals or exceeds the specified breakpoint value. This
breakpoint is set using the SET_POS_BRK command.
A 32 bit position breakpoint can be specified which will result in
the parameters being updated when the current target position
(the instantaneous desired axis position output from the profile
generator) equals or is less than the specified breakpoint
value.This breakpoint is set using the SET_NEG_BRK command.
A 32 bit position breakpoint can be specified which will result in
the parameters being updated when the current actual position
(the instantaneous position of the actual axis hardware) equals or
exceeds the specified breakpoint value.This breakpoint is set
using the SET_ACTL_POS_BRK command.
A 32 bit position breakpoint can be specified which will result in
the parameters being updated when the current actual position
(the instantaneous position of the actual axis hardware) equals or
is less than the specified breakpoint value.This breakpoint is set
using the SET_ACTL_NEG_BRK command.
A 32 bit time breakpoint can be specified which will result in the
parameters being updated when the # of cycles executed since
chip set reset (the current chip set time) is equal to the time
breakpoint value.The # of cycles continuously increases until it
rolls over from 2 32 - 1 back to 0.The time breakpoint is set using
the SET_TIME_BRK command.
23
Motion Complete Breakpoint
External Breakpoint
Normally, whenever one of these conditions has been programmed and
the condition occurs, the double-buffered parameters will automatically
be shifted to the active registers. There is a mechanism to disable this
"automatic update upon breakpoint" however. This is discussed in the
next section.
The above breakpoint modes are particularly useful during multi-axis
motion. This is because the next profile commands (set of host-
specified trajectory commands) can be pre-loaded and activated at the
precise position or time required, with no delay incurred to send an
update or load parameters command.
After a breakpoint condition has been satisfied it is no longer
active. To set up another breakpoint condition, a new one must be
explicitly set by the host.
The double-buffered registers that are shifted to the active
registers do not change upon being shifted, only the active
registers change.
Except for the MULTI_AXIS command, parameter loading and updating
is controlled individually for each axis. In addition each axis has a
separate 32-bit breakpoint register, and can be set to various individual
breakpoint conditions.
External Breakpoints and Homing
By connecting a home input sensor to the home signal input of the
MC1451-series chipsets it is possible to cause the chipset to halt a
motion at the moment it receives the home signal. This capability
makes it ideal for performing a home sequence. The following host I/O
sequence illustrates this:
GET_HOME
SET_POS 12345
SET_VEL 23456
SET_ACC 345
UPDATE
SET_EXT_BRK
A breakpoint can be specified which will result in the parameters
being updated when the previous motion has been completed
(motion complete bit is set). When using this breakpoint no 32 bit
compare value is required.
A breakpoint can be specified which will result in the parameters
being updated when the home signal of the corresponding axis
becomes active (low). When using this breakpoint no 32 bit
compare value is required. This breakpoint is useful whenever it is
desired that an external signal starts, stops, or otherwise modifies
the profile movement.
; check to make sure axis not already at
; home. If so, then a 'reverse' move must
; be made to retract axis from home switch.
; This ‘reversing’ sequence is not
; indicated here for simplicity sake
; load home move parameters
; start home move
; initiate external breakpoint mode