Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 178)

Publication 1747-UM010B-EN-P - September 2003
A-14 Specifications
Backup Scanner Output Delay Time (T
SNo
) Tables
The tables provided in this section show the maximum backup
scanner output delay time (T
SNo
) for specific applications. T
SNo
is
dependent on the following:
•
processor scan time, or time between immediate outputs (if no
BTs are present)
•
number of logical racks configured
•
whether normal or complementary I/O mode is selected
•
RIO baud rate (if complementary I/O is selected)
T
SNo
increases if the interval between T
upd
decreases to the time
threshold (T
hold
). If T
upd
is less than T
hold
, then the larger T
SNo
number must be used. Otherwise, either number may be used.
Determining the Number of Logical Racks Configured
The number of logical racks configured is determined by the number
of racks that contain configured devices. For example, if there are
four 1/4 rack devices in logical rack 0 and one full rack device in
logical rack 3, there would be two logical racks configured. The
number of logical devices on the RIO network affects only T
RIO,
and
only affects T
SNo
when additional logical racks are used.
When complementary mode is selected, the number of configured
racks is also determined by the number of primary or complementary
racks configured, but not by both. (The maximum number of
configured racks is 4.) That is, if there is a primary rack configured
with a corresponding complementary rack, that is considered one
Variable Variable Description
T
SNo
The maximum scanner output delay time
T
upd
The time between SLC processor output scan updates or immediate output
updates
T
hold
A constant time threshold that is dependent on your configuration. Refer to
the table on page A-15.
IMPORTANT
The times shown in this section are, to the best of our
knowledge, the maximum delay times of the backup
scanner. However, in instances that throughput is an
important consideration, test the application
thoroughly first to ensure proper operation. In most
situations the average throughput is much better than
the calculated maximum throughput.