Rockwell Automation 1771-SDN DeviceNet Scanner Module Installation Instructions - Manual (Page 24)

Publication 1771-IN014B-EN-P - September 2001
24 DeviceNet Scanner Module Catalog Number 1771-SDN/C
Device Active Table
The Device Active Table is located in words 0–7 of a 51 word BTR.
The scanner assigns one bit of the first 128 bits to each device on the
networks. The scanner assigns one bit to consecutive Device
Addresses.
Devices on Channel 1 are indicated by a single bit in consecutive
order in words 0–3. Devices on Channel 2 are indicated by a single bit
in consecutive order in words 4–7.
If a bit is set, it indicates that the node is in the scanner’s scan list and
has successfully communicated with the scanner. These bits are not
cleared if the slave node goes off-line. The bits are cleared by
resetting the scanner.
Device Failure Table
The scanner maintains one Device Failure Table accessed with a
52-word BTR. The table consists of:
•
Communications Failure Bitmap – the scanner tracks device
failures in its scan list by assigning one bit of the first 128 bits in
the table to each device on the networks. The scanner assigns
one bit to consecutive Device Addresses. Devices on Channel 1
are indicated by a single bit in consecutive order in words 0–3.
Devices on Channel 2 are indicated by the bits in words 4–7.
If a bit is set, it indicates that the node is in the scanner’s scan
list and is either not present, not communicating or failed
autoverify.
•
Autoverify Failure Bitmap – the scanner tracks autoverify failures
by assigning one bit of the second 128 bits in the table to each
device on the networks. A value of 1 in the bit position indicates
a failure is detected and a value of 0 indicates normal operation.
The scanner assigns one bit to consecutive Device Addresses.
Devices on Channel 1 are indicated by a single bit in
consecutive order in words 8–11. Devices on Channel 2 are
indicated by the bits in words 12–15. If a bit is set, it indicates
that the device is returning device keying or a data size that
does not match the keying or data size in the scanner
configuration table.
•
DeviceNet 1 Scan Counter (word 16) – the scanner increments a
one-word counter whenever a scan of the DeviceNet 1 devices
is completed. The counter rolls over when it reaches its
maximum value.