MC1151A PMD, MC1151A Datasheet - Page 29

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

Note that it is not required to process multiple interrupts separately (as
is shown in the example). It is perfectly valid to process 2 or more
interrupt conditions at the same time, and to then send a RST_INTRPT
command with a mask that clears multiple bits at the same time.
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.
Pulse & Direction Signal Generation
For each axis two signals are provided which determine the desired
axis position at any given moment. These two signals are the pulse
signal, and the direction signal.
The pulse signal output by the chipset consists of a precisely-controlled
series of individual pulses each of which represents a desired
increment of movement. This signal is always output as a square wave
pulse train (50 % duty cycle regardless of pulse rate).
A step, or pulse, is considered to have occurred when the pulse signal
transitions from a high to a low output value
The direction signal is synchronized with the pulse signal at the
moment each pulse transition occurs. The direction signal is encoded
such that a high value indicates a positive direction pulse, and a low
value indicates a negative direction pulse.
The MC1451-series of chipsets supports two separate pulse rate
modes, known as the standard speed mode, which can output pulses at
up 48.8 KSteps per second, and the high speed mode, which can
output pulses at up to 1.5625 MegaSteps/sec.
For full-step and half-step applications, as well as pulse and direction
applications which will have a maximum velocity of ~ 48 ksteps/sec, the
standard speed range should be used. For applications which require
pulse rates higher than 48 ksteps/sec the high speed range should be
used.
To select the standard speed mode use the command
SET_OUTPUT_STNDRD. To select the high speed mode use the
command SET_OUTPUT_HIGH. Speed range is selectable separately
for each axis.
To read back the current speed range setting, use the GET_MODE
command, bit # 9.
The pulse counter is designed such that a step occurs when the
pulse signal transitions from high to low. Systems that use step
motor amplifiers that interpret a pulse as a low to high transition
should insert an inverter at the pulse signal output from the
MC1451A chipset to insure proper step counting.
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Pulse Generation Control
The rate of pulse output is usually determined by the particular
trajectory profile parameters being requested by the host processor.
In addition to the trajectory profile however there is separate method of
enabling and disabling pulse generation. This method is known as
'motor control' and provides an on/off pulse generator control
mechanism. The command to enable pulse output is MTR_ON and the
command to disable pulse generation is MTR_OFF.
MTR_OFF causes the trajectory generator to immediately discontinue
further pulse generation until a MTR_ON command is given. As long as
the motor is in the off state any further trajectory commands will have
no effect until the motor is turned on.
The current motor status (on or off) can be read back using the axis
status word (bit # 8).
It the motor is turned on by the host (MTR_ON command) the motor will
stay at rest until a new trajectory move is loaded and initiated.
In addition to manually turning the motor output on and off it possible for
the chipset to automatically turn the motor off during a motion. This can
occur if the chipset detects a motion error condition while the auto-stop
feature is enabled. See the section of this manual below entitled "Stall
Detection" for more information.
At Rest Indicator
In addition to the standard pulse and direction output signals the
MC1451-series chipsets provide an additional output for each axis
known as the AtRest signal which indicates when the trajectory
generator is in motion.
This signal can be useful when interfacing with amplifiers that support a
separate torque output level for the stepper during motion as when the
motor is not moving (holding).
This feature is enabled and operational automatically at all times. It
does not need to be initiated by the host processor.
Encoder Position Feedback
The MC1451A-E version of the MC1451A chipset has the capability of
receiving quadrature position data so that the current location of the
motor can be determined.
To receive quadrature information the MC1451A chipset must have the
optional 'ENC' chip installed.
The MC1451A-E supports two encoder signals per axis, the A
quadrature channel and the B quadrature channel. Up to four axes are
supported. For a given chipset the number of encoder channels
supported is equal to the number of pulse and direction channels. For
example the MC1251A-E supports 2 sets of pulse and direction
channels and 2 sets of A, B quadrature signals.