Micrologix 1200 retentive bits

Hi
i am wanting to know if there are any bits you can use in the plc ladder that remeber there state if the power is removed from the plc ie retentive or battery backed??
Alex
 
Any bit which is turned on by an OTE (and was on at power down) will be reset on power up. If it was turned on by an OTL (and was on at power down) then it will still be on after power up.

In essence the start-up runs through the program evaluating the end of each rung as if the rung was evaluated as false. This turns off OTE's but leaves OTL/OTU pairs alone.
 
In the AB PLC's, including SLC's, Micrologix, CompactLogix, FlexLogix, ControlLogix, and PLC5's, ALL data is by default retentive. You don't need to latch them, just setting bits in the data tables (classic) or tag browser (Logix), they will hold the state as long as the backup battery holds.

Note that you can also set things offline, and they will be downloaded.

As mentioned above though, anything driven with an OTE instruction is auto-cleared on the first-scan when going into run.
 
Its funny reading these threads after a period of time. As I was reading I was thinking exactly what rdrast said. I would add one thing.

The data is all retentive by nature. I know some PLCs have certain locations that are retentive and other locations are non-retentive. That is not the case with A-B PLCs. If you open any data file and type a one in any bit location then cycle power that one would still be there.

However, once you start writing logic or adding I/O modules they want to start manipulating that data. Instructions that are considered retentive (like the latch) will leave the data alone during what is called the pre-scan. Thus a latched output would still be latched following a power cycle. Non-retentive outputs are affected during the pre-scan. So an OTE turns off, a TON resets, etc.

Following the pre-scan the data will be affected by logical state of your program and by I/O modules.

Hope I didn't confuse matters further.

OG
 
No, but it's getting over complicated I think. Any data in the register is retentive unless it is used in the code. It just all depends on the program.
 
I use integers bits, (an integer is made of 16 bits) if I want to save a bit state thru a powerdown/up. Though I can't swear to the MLX1200 ... I've only used it on MLX1000 & 1500.
 

Similar Topics

Hi everyone, I'm working on a project where I need to exchange data between a Siemens S7-1200 PLC and an Allen-Bradley MicroLogix 1400 PLC. The...
Replies
8
Views
486
I have a MicroLogix 1200 that has an 8 input and a 16 output. Every 6 months-year I get a fault and when online go to error it is something like...
Replies
3
Views
448
Have a bad output on a Micrologix 1200. Moved wire over to an available output, changed program to associate with new output. downloaded program...
Replies
8
Views
728
I need help achieving the following task: ML1200 sending 4 to 20 mA thru analog output ch0 to a DC speed controller analog input(4 to 20 mA) my...
Replies
3
Views
649
Hi there I am new with this thing and i don't know how to connect Allen Bradley Micrologix 1200 PLC to Raspberry Pi using USB to RS485 in NodeRED...
Replies
3
Views
2,232
Back
Top Bottom