Hello Nimal, Thank you for contacting National Instruments! The reason that you are experiencing this problem is because the Traditional NI-DAQ driver is single-threaded. Your Cont handshake input VI has a DIO Read VI inside a while loop with no wait. When this VI runs, the DIO Read VI will wait until it has acquired all of the Scans to Read and then will release the driver to be used by your position measurement. The VI will either read the number scans in the backlog or the number of scans to read. Since you do not have a wait, it is likely that the scan backlog is alway nearly zero. This means that the DIO Read VI will almost always be waiting for the total number scans to read before it releases the driver.
You can do a couple things to alleviate this problem. 1. Place a delay inside your Cont. Handshake input VI's while loop. This will cause your backlog to grow. Do not use too large of delay for your scan backlog will grow out of control and overflow the buffer. 1 - 10ms should work fine. 2. The best way to solve this problem is to combine the two VIs into a single VI. This way, you can use the error cluster to control when things execute. You can have both sets of code in parallel and then snake the error cluster from the first set of code to the next. This will cause the DIO code to get configured first then the counter code and then in the loop, you would run the error cluster to the DIO Read and then to the counter get attribute to read the position. This would ensure that both measurements had equal time. The easiest thing to try is to decrease the scans to read in the Cont Handshake input and insert a delay in the while loop. Let me know if you are successful. Regards, Bill B. Applications Engineer National Instruments"
