Clock Memorybyte in Siemens S7 CPU

userxyz

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Bit of the Clock Memory Byte

7

6

5

4

3

2

1

0

Period Duration (s)

2.0

1.6

1.0

0.8

0.5

0.4

0.2

0.1

Frequency (Hz)

0.5

0.625

1

1.25

2

2.5

5

10




so bit 7 is 1s, but how can u see this, if u want to know bit 5 for example

possibly a stupid question,...
 
Just set up the address of the marker byte you want to use as the clock memory, usually MB0 is default but you can select whatever you want.

reload your PLC with the harware profile with this set and then look at the MB you chose in a VAT table, you will see all the bits toggling.
 
What you have to do is..

From the Hardware configurator you must open the CPU properties. When the window opens, select the "Cycle/Clock Memory"-tab.

The last section on this tab is titled "Clock Memory". You must check the "Clock Memory"-box and type the number of the memorybyte you want to use in the other box.

If you type one(1) and download the configuration to the PLC you can now use the clock memory byte in the program. For example M1.1 will blink at 10Hz frequency and M1.7 at 0.5Hz frequency.

I hope this was your question.
 
Hey

I know how to configure the clockmemorybyte,

but, I need to know:

Pulse every 1.6 secs, every second, etc... how can u calculate or see this ?
 
Hey

what I basically need is a pulse every second,

MB0 = memorybyte

bit 0.7 =
Period Duration (s)
2.0
Frequency (Hz)
0.5

So bit 7 is pulse/second ? In a VAT it's like a second, bit 7, but need to be sure
 
With the bit M0.7 I think that it is "1" for 1 second and changes to "0" for 1 second. That would make the full cycle duration 2 seconds and frequency 0.5Hz because a "positive edge" is generated every 2 seconds.

That what I think but I dont have a PLC to test it.
 
I find the clock memory byte more useful as one-shots than its natural 50% duty cycle format:

Code: 
L	MB 101	  //Clock memory byte previous scan value
L	MB 0	  //Assigned clock memory byte
T	MB 101
XOW
L	MB 0
AW
T	MB 100	  //Clock memory byte one shot flags
 
Last edited:
Hey

Can you explain a bit what u wrote...



What I need is a pulse every second, bit 7 in de clockmemorybyte ist the right one

I think, bit number 5 is what I need, but I must be sure,

If I had 3600 pulses, than the time elapsed should be 1 hour, its for preventing of using timers
 
Combo,

Bit 5 is the one you want. It'll be on for 0.5s and off for 0.5s.

So in 1 hour you will have 3600 times the on level (and of course 3600 times the off level).
 

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