Rockwell Automation 1788-CN2FF ControlNet-to-FOUNDATION Fieldbus H1 Linking Device User Manual User Manual

Page 37

1788-6.5.1 - January 1999

Using the ControlNet-to-FOUNDATION Fieldbus H1 Linking Device

4-11

Figure 4.8 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).

Bit Position

Value

Acknowledge

CLEARED

ACTIVE