Hello all experts.. i am new to this field of PLC. Can anyone one explain me the meaning of the term "merker bit" associated with PLC programming (better if explained with reference to Siemens PLC)?

 

"merker bit" is german.
You may translate merker to memory.
It's a variable in memory that can store 1 bit.

 

Hi!

A so called "merker bit" is a bit that does not interface the hardware IOs. it's something like a flag to store information.
gtx

werna

 

Try Flag. Merker is German and litterally means Marker (The sign, not the writing tool). The flag/merker is inherited from the S5 as a global memory range for free use. It goes against the concept of object oriented or even modular programming but exists mainly as a legacy for compatibility reasons. The use in S7 programs is not promoted and is considered bad programming.

Merkers like inputs and outputs are organised in bytes and the user has direct access to the bits.
e.g. MB 2 is Merker byte 2
MW 2 is Merker word 2 (byte 2 and byte 3)
M2.0 is bit 0 in Merker byte 2
M2.1 is bit 1 in Merker byte 2
etc...

 

In the Siemens world there is no Timer Done bit as in the AB world. So at the end of the timers there is an real bit. When our German friends translate AB programs they take the timer done bit and turn on a "Merker bit" (translated Marker Bit). This adds unneeded memory useage but does speed the translation.

 

A Merker bit is a free usable bit
Use it as a single bit faor example M 0.0
or as a byte example MB 1 or MB 0
or as a word MW 0 or MW 2
MW 0 contains MB 0 and MB 1
MW 2 contains MB 2 and MB 3

so as you see it's not recommended to use MW 1 aldo you can, but it is good practice to use only even words.

 

Hello,

merker bit = memory bit (M)

Good luck!

 

Moin PLC crazy,
moin all,

A "merker bit" is German for a memory bit.

BTW, Siemens also has English manuals.

regards
Friedrich Haase

 

Actually it is Maerker ("ae" = Umlauted a; - meaning roughly equivalent to semaphore) - it is equivalent to an iternal coil - you can set its, reset it, read it - but it does nothing outside the PLC (an internal binary variable).

Meir

 

Hi,
I think you could be a little confused,

In SIMATIC mode, timers may be referenced as bits or timer values, if you reference T100 as a BIT, then it returns the 'TIMER DONE' if you
reference it as an INTEGER, then it returns the ELAPSED TIME.

Of course nowadays we have IEC1131-3 mode, (which is strongly data typed where SIMATIC is not) global variable need to be typed, so you
must specify an OUTPUT 'TIMER DONE' BIT, and an ELAPSED TIME 'CURRENT VALUE' (Last time I looked AB supported IEC1131-3 too, one world

http://tinyurl.com/6wb3n

http://www.plcs.net/

http://www.siemens-usa.com/You_know_Siemens/

Marc Sinclair

 

They do?? :^)

Regards
cww

 

According to the Siemens German to English dictionary a merker is: "bit memory, marker|| flag|| marker..." So it is an internal, discrete, binary storage location, used for "dummy" flags that do not directly correspond to any real world device or function.