Rockwell Automation 1771-SF1 SERVO INT MOD - Manual (Page 13)

Chapter
3
3Ć1
Programming and Operation
The servo interface module controls the operation of a single motor servo
drive package in accordance with commands received from the micro
controller. Outputs to the servo amplifier of the drive package include:
-10.000 to 9.995V analog output signal for proportional motor speed
and direction control.
A TTL output to limit the drive current from the servo amplifier to the
motor.
A TTL output signal to turn the servo amplifier ON or OFF.
The servo interface module also monitors motion by counting quadrature
pulses from a shaft encoder. The pulses represent the rotational position
of the encoder shaft or servo motor drive shaft. The servo interface
module sends an interrupt signal to the micro controller every time the
accumulated counts of quadrature pulses equal a preset target value. This
signal can be used to minimize the programming required to monitor and
control the position of the drive shaft.
Differential line drivers convert the single-ended encoder signal to
differential pulses for Channels A, B, and Marker of the module. The
driver also transmits a complement set of pulses (equal but logically
opposite) to Channel A, Channel B, and Marker channel.
All data transfers between the micro controller and the servo interface
module take place over the normal I/O 8-bit data bus on the backplane of
the 1771 I/O rack. The transfer of each one of the following data bytes is
initiated by a separately addressed read or write instruction from the
micro controller. The enable commands are transmitted over the special
DSEN lines described in the Micro Controller User’s Manual (Publication
No. 1771-6.5.5).
The servo interface module contains a Digital to Analog Converter (DAC)
that sends a 0 to +10V analog voltage to the servo amplifier of the motor
drive package. The voltage controls the speed and rotational direction of
the servo motor. The input to the DAC is a 12-bit binary number sent
from the micro controller that allows the speed and rotational direction of
the servo motor to be changed by user program. The DAC converts the
General
Data Transfers
DAC Data (Servo Motor Speed)