mc1451a-e ETC-unknow, mc1451a-e Datasheet - Page 31

• Manufacturer Part Number: mc1451a-e
• Description: Advanced Brushless Motor Control Chipset
• Manufacturer: ETC-unknow

The RST_INTRPT and GET_I commands are only effective when
there is an interrupt present. If no interrupt is present than
alternative 'polled-mode' commands such as RST_STATUS or
GET_STATUS should be used.
Encoder Position Feedback
The MC1231A-series of chipsets support direct input of incremental
encoder signals. Four position input and control signals are supported:
The A and B signals are used to continuously maintain the position of
the motor, and the index and home signals are used as trigger inputs to
a high-speed position capture mechanism.
Each quadrature channel consists of a square wave offset 90 deg. from
the other. Positive motion consists of the A channel leading the B
channel by 90 deg., and negative motion consists of the A channel
lagging the B channel by 90 deg. For each full phase of one channel,
four resolved quadrature counts will occur, resulting in a 4 to 1
resolution enhancement over the basic channel resolution.
The index pulse is typically located on the encoder and will be active
once per revolution. The chip set recognizes that an index trigger has
occurred (i.e. when the 32-bit index location is captured) when the
index signal, as well as the A and B signals transition low.
The home signal is typically connected to a position reference sensor,
or to any other general purpose synchronizing signal. The home signal
is recognized when it alone transitions low. The state of the A and B
signals does not affect home signal trigger recognition.
Encoder Filtering
To enhance reliability of the received encoder information the MC1231A
provides digital filtering of the quadrature data lines (A and B
quadrature count) as well as the index and home signals.
For all of these signals a valid high or low condition is recognized only
when the condition has been maintained for 3 clock cycles of 160 nSec
each (total required duration of 480 nSec)
For example if a brief spurious noise signal on one of the lines occurs
for 300 nSec, then this noise will be rejected until a valid state change
lasting over 480nSec occurs.
- A quadrature channel
- B quadrature channel
- Index pulse
- Home signal
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High Speed Position Capture
Each axis of the MC1231A supports a high speed position capture
register that allows the current axis location to be saved using an
external trigger signal. When in incremental encoder mode, The
MC1231A allows either the index signal or the home signal to be used
as the capture trigger. These two input triggers differ however in that
the index signal will cause a position capture when it, as well as the A
and B index signals, transition low, while the home signal will result in a
capture when it alone goes low.
The commands SET_CAPT_INDEX and SET_CAPT_HOME select
which input signal is used.
After an index or home signal has been captured by the MC1231A, the
capture value must be read by the host processor before another
position capture can occur. In addition, if the index signal is being used
as the trigger, the index signal,along with the A and B quadrature
signals, must transition high before another index pulse can be
registered.
The captured position is equal to the axis position at the moment the
trigger pulse was encountered. Note that the capture register is located
in hardware. Its accuracy is therefore not affected by the velocity of the
axis.
Index Pulses And Commutation
In addition to providing one of the two sources for the high speed
position capture the index-signal has an additional function which is to
maintain synchronization during commutation.
Although this function is optional, if connected, the index signal can
improve the reliability of sinusoidal commutation by eliminating any long
term drift due to lost encoder counts. To utilize this function it is simply
necessary to use an index pulse which occurs once per motor rotation
(rotary motor), or at the same point within the commutation electrical
cycle (linear motor). For more information see the section of this
manual entitled "Sinusoidal Commutation".
Motor Outputs
The MC1231A series of chipsets provides two different motor amplifier
interfaces:
The output mode is host-selectable. The selected method affects all
axes (motor output mode is not individually programmable for each
axis). The host commands to select these output modes are
SET_OUTPUT_PWM (to select PWM mode), and
SET_OUTPUT_DAC16 (to select 16 bit DAC mode).
- 10-bit 24.5 Khz PWM interface
- 16-bit DAC output.