Do we need to manually unlatch motion instruction bits ?

[Joseph 0028 0]

I have seen some programs in which they manually unlatch all bits like in figure 1, and in some programs they don't do that. 

The instruction help page, ladder execution says that in pre-scan .EN, .DN, .ER, .IT bits are cleared to false

So do we need to unlatch all these bits before giving a motion command like MAM ?

 

[panic mode 245]

i have never seen successful installation where end user has to look at ladder code and manually toggle some bits. programmer may relay on that during development but this is clearly not a way to run any system. anything that need to be initialized for proper operation need to be done in program before every use.

[Joseph 0028 0]

So we need to unlatch these bits before every motion command ? 

Cause i have seen programs without unlatching these bits, but they still work fine. So just wanted to know if its really necessary. 

[pturmel 140]

It is not necessary.  Though it is common to unlatch the .ER bit from separate fault reset logic as a convenience.  The instruction will initialize all of those bits correctly on the rising edge of the rung.  Prescan isn't actually relevant.

Edited 7 Jul 2021 by pturmel
Clarification

[Joseph 0028 0]

@pturmel that answers it, thank you.