How to control DQ signal more exactly.

Hi all,

I checked I can control DQ signal every 2ms by oscilloscope at the condition below.

1.H/W

A. IPC647C operated by WinAC RTX – I think S7-300 CPU would show same performance.

B.ET200SP with some DQ standard IO

2.S/W – TIA Portal V12 SP1 – I think it doesn’t matter

3.Program

A. OB3X (cyclic OB)

i. Code is attached.

ii. As you knew, Timer make difference more bigger.

iii. For check signal accuracy, I changed OB cyclic period.

1. For example, when check whether signal last 10.00ms or not, I changed OB cycle period to 10ms

B. PIQ are also updated by thisOB period

Weird thing is that I can’t control odd number cycle period like as 3ms, 5ms and 11ms. Even though controller can control signal by 2ms sharply.For example, when command that DQ signal 3ms On then, 3ms Off, it acts 4.003ms On 1.998ms Off. Signal acts as if they can’t act by odd cycle(attachment:Oscilloscope is chaptured).

My question is

1.Why can't I control DQ signal by odd number ms time duration in this configuration? what is problem in this configuration?

2.Plus Can we control DQ signal by 1ms accuracy with standard distributed IO? If yes, how to configure the system?

Thank you for your helps in advance.

I found missing point. That is setting of IO update time. Please my attachment. After setting update time to 1ms, it works at odd(3,5,7..) cycle time.

Next I tested 1ms On/Off toggle program.Even though CPU longest execution time was only 0.3ms, it doesn’t work. It seems error happen during interface of profinet RT. As we knew, 1ms update time is just minimum not guaranteed.

If we needs better performance, we have better recommend IRT module(for guarantee of under 250us) .