A single bit digital status reads a value of 0 or a 1 from one address on an I/O device. An example of a single bit digital status would be a pump's status, where the pump is either off (0), or on (1).
A double bit digital status reads a value of 0 or 1 from two addresses on an I/O device. An example of an equipment process requiring a double bit digital status might be a valve with 4 states: open, closed, open or close action in progress, or error. The table below indicates the possible values for a double bit digital status according to the values at each bit.
|
State |
Bit 1 Open |
Bit 0 Close |
Description |
Tag Value |
|
State 0 |
0 |
0 |
A process is in action (either the valve is opening, or is closing) |
0 |
|
State 1 |
0 |
1 |
The valve is closed. |
1 |
|
State 2 |
1 |
0 |
The valve is open. |
2 |
|
State 3 |
1 |
1 |
There is an error. |
3 |
|
Invalid |
Invalid |
Invalid |
No data. |
Invalid |