Rockwell Automation 1771-SF1 SERVO INT MOD - Manual (Page 16)

Programming and Operation
Chapter 3
3Ć4
A write instruction to memory location 600FH latches these bits. DSEN
Line 17 enables the transfer from the servo interface module. The control
byte is reset at power-up or whenever the data byte reset command is
programmed.
The encoder line drivers generate pulses for each encoder line. Assume
that a 250 line encoder is used as in Figure 2.2. When the quadrature
multiplier is x1, a counter increment of 1 means that the encoder shaft has
turned through 1.44
o . (This can be translated into the linear movement of
a feed slide, proportional to the number of drive shaft threads per inch.)
When either the x2 or x4 quadrature multiplier is used, one count is
equivalent to a turn of .72
o or .36 o , respectively.
The micro controller can be programmed to read the accumulated value of
the encoder counters in the servo interface module by a read instruction
from memory location 6008H. A read from the encoder counters is
usually performed when the encoder is halted or turning very slowly. A
read from this location does not halt counter operation. DSEN Line 10
enables the transfer from the servo interface module. The encoder
accumulated value is set to zero at power-up and after 255 counts. It also
can be set to zero by the counter reset command which is a write to
location 6009H.
The target value determines at which count (in the accumulated count of
encoder pulses) an interrupt will be sent to the micro controller. The
target value is an 8-bit comparator preset ranging from 0-255. Target
value interrupts can be counted to monitor and control the rotational
position of the drive shaft.
A write instruction to memory location 600CH latches the target value.
DSEN Line 14 enables the transfer from the micro controller to the servo
interface module. The target value preset is reset to zero at power-up or
by the data byte reset command (write location 600BH).
Four special backplane lines are used to monitor servo signals at the micro
controller. The first three lines transmit the marker, A>B, and CCW/CW
signals, respectively, to the status port of the micro controller. They are
read at memory address 7000H. These signals are always on-line. The
fourth line transmits the interrupts to the micro controller.
Encoder Counter Values
(Position Pulses)
Target Values (Position
Interrupts)
Special Servo Lines on the
Backplane