Reference Manual

PMAC 2 Software Reference
124 PMAC I-Variable Specifiation
Remarks
Ix93 tells Coordinate System x where to look for its time base control (feedrate override)
information by specifying the address of the register that will be used. The default value
of this parameter for each coordinate system (see above) specifies the register that
responds to on-line commands. If the time base is left alone, or is under host or
programmatic control, this parameter should be left at the default.
Alternatively, if the time base is controlled externally from a frequency or voltage, the
register containing the time-base information will almost always be in the conversion table
(which starts at address $720 [1824 decimal]). With the default conversion table, there is a
time-base register at $0729 (1833) related to the frequency into the Encoder 4 counter.
This frequency can be controlled by an input voltage on the WIPER pin of the Control
Panel Port if jumpers E72 and E73 are ON. If another register is to be used for the time
base, it must have the units of I10 so that 8388608 (2
23
)
indicates 1 msec between servo
interrupts. See instructions for using an external time base, under Synchronizing PMAC to
External Events.
Note:
Ix93 contains the address of the register that holds the time-base
value (it is a pointer to that register). Ix93 does not contain the
time-base value itself.
See Also
Time-Base Control (Synchronizing PMAC to External Events)
Control Panel Port Inputs (Connecting PMAC to the Machine)
I-variables I10, Ix93, Ix95
On-line commands %, %{constant}.
Jumpers E72, E73
Ix94 Coordinate System x Time Base Slew Rate
Range
0 .. 8,388,607
Units
2
-
23
msec/ servo cycle
Default
1644
Remarks
Ix94 controls the rate of change of the coordinate system’s time base. It effectively works
in two slightly different ways, depending on the source of the time base information. If
the source of the time base is the “%” command register, then Ix94 defines the rate at
which the “ (actual time base) value will slew to a newly commanded value. If the rate is
too high, and the % value is changed while axes in the coordinate system are moving, there
will be a virtual step change in velocity. For these type of applications, Ix94 is set
relatively low (often 1000 to 5000) to provide smooth changes.
Note:
The default Ix94 value of 1644, when used on a card set up with the
default servo cycle time of 442 µsec, provides a transition time
between %0 and %100 of one second.
If there is a hardware source (as defined by Ix93), the commanded time-base value
changes every servo cycle, and the rate of change of the commanded value is typically
limited by hardware considerations (e.g. inertia). In this case, Ix94 effectively defines the
maximum rate at which the % value can slew to the new hardware-determined value, and
the actual rate of change is determined by the hardware. If you wish to keep synchronous
to a hardware input frequency, as in a position-lock cam, Ix94 should be set high enough
that the limit is never activated. However, following motion can be smoothed significantly
with a lower limit if total synchronicity is not required.