Rockwell Automation 1734-SSI POINT I/O Synchronous Serial Interface Absolute Encoder Module User Manual - Manual (Page 30)

Publication 1734-UM007D-EN-P - December 2005
4-2 Set and Operate Your Module
Data Rate The data rate is the SSI sensor’s communication rate
(bits/s) stated in the manufacturer’s data sheet.
The data rate you select at the SSI module equals the
approximate frequency of the SSI module’s clock output
(the actual measure frequency varies with the SSI word
delay time).
The maximum data rate that can be used for your
application is limited by the transmission line length
between the SSI module and sensor.
See the SSI sensor data sheet, as well as the 1734-SSI
Installation Instructions, publication 1734-IN581, for
communication rate versus transmission line length
information. The module supports the following SSI data
rates: 125, 250, 500 Kbps, 1 and 2 MBps.
The module default rate is 125 Kbps.
Gray-to-Binary Conversion The 1734-SSI module can change the displayed SSI sensor
data from Gray to Binary. Change this setting to ON only
when using a Gray-code sensor and you wish to read a
present SSI value that is proportional to total sensor travel.
Gray-code sensor values continuously increase and
decrease as the sensor travels in one direction, and do not
provide a sense of proportionality. The module default for
this setting is OFF.
SSI Word Delay Time This is the time between successive SSI words that are
transmitted by the SSI sensor to the module. The 1734-SSI
module features a wide selection of delay times ranging
from 16…64,535
µs. The module default delay time is
64 µs. Refer to your SSI sensor data sheet for the
recommended delay time. If the sensor manufacturer
specifies a value called monoflop time, use that value for
the SSI word delay time setting.
SSI Word Filter Control The number of successive, equal SSI data words received
by the module from the SSI sensor in order to update the
real-time present SSI data word. Max = 5 successive equal
values, High = 4, Med = 3, Low = 2, and Off = the module
produces a SSI data word each time a new value is
available from the SSI sensor, without the previous value
comparison. Adjust the SSI Word Filter Control value when
using SSI sensors with the Position Forming time
< 0.5 ms, so that you can see SSI sensor data change as the
sensor is in motion.
Note that changing the default value of 5 (Max) for this
parameter is done at the expense of reporting accurate
sensor data in an electrically noisy environment.
Data Standardization You can remove bits from the right side of the displayed SSI
present value word by setting Data Standardization to ON.
This feature can be used as a divide by a power of two, or
for data masking. Enter the number of bits you wish to
remove in the Trailing Bits parameter (discussed below).
The default setting for Data Standardization is OFF.
Trailing Bits The number of bits removed from the displayed SSI present
value word if Data Standardization is ON. The range is
0…16 bits, and the default value is 0.
Value Definition