Turbo PMAC Users Manual Manual

Delta Tau Turbo PMAC User Manual
PFM Pulse Width: I7m04, I6804, MI904, MI908, MI994
The width of the output pulse is controlled by the PFMCLK frequency with I7m04 for the channels on
Servo IC m, I6804 for the channels on MACRO IC 0, or MI904, MI908, or MI994 for the ICs on a
MACRO Station. This I-variable specifies the pulse width as the number of PFMCLK cycles. At the
default PFMCLK frequency of 9.83 MHz, the default value of 15 produces a 1.5-µsec output pulse width.
This should be satisfactory for most MLDT devices. When using the RPM format or equivalent (see
Signal Format, above), the pulse width must be large enough to enclose the rising edge of the returned
“start” pulse – that is, it must be longer than the delay between the output pulse and the returned start
pulse.
PFM Format Select: I7mn6, I68n6, MI916
The output format of channel signals is controlled by variable I7mn6 for Servo IC m Channel n, by I68n6
for MACRO IC 0 Channel n, or by node-specific variable MI916 on a MACRO Station. In order for the
C-register circuitry of Channel n to output a PFM pulse train rather than a PWM pulse train, this variable
must be set to 2 or 3. Most commonly, it will be set to 3, so that the A and B registers for Channel n
output DAC signals rather than PWM.
Note:
You cannot use one channel of Turbo PMAC simultaneously for direct PWM
control of a motor, and for MLDT pulse generation. Direct PWM control of a
motor automatically writes to the channel’s A, B, and C registers every phase
cycle.
MLDT Feedback Select: I7mn0, I68n0, MI910
The decoding of the signals on the “encoder” inputs is controlled by I7mn0 for Servo IC m Channel n,
I68n0 for MACRO IC 0 Channel n, or by node-specific variable MI910 for a channel on a MACRO
Station. For proper decoding of the MLDT signal, this variable must be set to 12. With this setting, the
pulse timer is cleared to zero at the falling edge of the output pulse. It then counts up at 117.96 MHz until
a rising edge on the return pulse is received, at which time the timer’s value is latched into a memorymapped
register that the processor can read. This register is the X-register at the base address of each
channel.
Note:
The MLDT feedback uses the same circuitry that would be used for quadrature
encoder feedback on that channel, so you cannot simultaneously connect an
encoder and MLDT to the same channel’s feedback on Turbo PMAC. In this
mode, it is the pulse timer that is used as a position measurement for feedback, not
the pulse counter that is used with encoders. The counter still registers the number
of pulses returned, but does not represent a position measurement here.
Conversion Table Processing Setup – Turbo PMAC Interface
The timer registers are processed in the conversion table as “parallel feedback” representing the position,
just as an absolute encoder would be. It is strongly recommended that you use the “filtered parallel read”
(method digit $3), to be able to reject errors due to extra or missing echo pulses. Consult Chapter 7,
Setting Up the Encoder Conversion Table in the User Manual and the specification for variables I8000 –
I8191 in the Software Reference Manual.
Setting Up Feedback & Master Position Sensors 4-19