Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 171)

Publication 1757-UM006A-EN-P - May 2002
Using the 1788-CN2FF, ControlNet-to-FOUNDATION Fieldbus H1 Linking Device 7-11
Each attribute corresponding to a process alarm has the three
alarm-related bits as shown in Figure 7.7.
Figure 7.7 Alarm Attribute Definition
Bits 7-3, DON’T CARE, are undefined when read and should be
ignored when performing a GET. The DON’T CARE bits should be
written as 0 when performing a SET. Bit 2, Acknowledge, is undefined
when read and should be ignored when performing a GET. When a
user wants to Acknowledge an alarm, this bit should be written as a 1
when performing a SET. Each time the LD detects a 1 in the
Acknowledge position, a Fieldbus Acknowledge will be generated.
Therefore, users must be careful not to set the Acknowledge bit more
than once per alarm. Bits 1 and 0, CLEARED and ACTIVE respectively,
are read/write bits.
When an alarm condition is ACTIVE or CLEARED, these bits are read
as a 1 when performing a GET. The user must Confirm each of these
states by writing them to a 0 by a SET. Once an alarm has occurred
(become ACTIVE), alarm processing is NOT complete until the user
intervenes to remove the alarm condition, Acknowledges the alarm
(writing a 1 in the Acknowledge bit position), Confirms the alarm
(writing a 0 to the ACTIVE bit position once it is read as a 1), and
Confirms the alarm condition being CLEARED (writing a 0 to the
CLEARED bit position once it is read as a 1).
Discrete Outputs This section describes configuration of the linking device to control
any discrete value (and status) in a Fieldbus device, such as in a
Discrete Output (DO) function block. It also describes the attributes of
the created ControlNet discrete output object.
The linking device contains one MDI block instances on each
Fieldbus channels. Each instance of the MDO block is the software
equivalent of a discrete output module in a I/O subsystem. Each MDO
block also has eight channels or outputs, with each channel
containing a byte and a status pair. Each MDO block has eight inputs
to provide for the BKCAL or readback from the discrete output
function blocks. The linking device assigns a tag to each MDO block
in the form CNetMacIdxx_DO_Modulei-j, where xx is the ControlNet
network address, i is the Fieldbus channel number, and j is the
module or instance number.
Bit Position
Value Acknowledge CLEARED ACTIVE
0 1 2 3 4 5 7 6
X X X X X