Synchronizing devices using zBusSync

Tech Note: TN0139
Product: ActiveX
Version: All
Date Added: 2004-09-01

Issue

There are several things to notice when synchronizing devices through the ZbusSync in ActiveX.

First, there is a crystal that drives the processor for each device. The crystals have small differences in their actual frequency, which is less than .001%. However, over several seconds this slight difference can have a large effect between racks that is in the milliseconds range. In order to remove this problem, all devices are driven by the same clock. For the gigabit interface the PI5 controls the clock. However, for the USB interface the clock is in the USB connection, which will often create more of a delay between racks.

The second issue is the start and stop time for devices. When two or more devices are running there will always be a slight delay between the start of one and the start of the other (several milliseconds).

Workaround

A ZBUSsyncA or B can be used to ensure that they are synced. This trigger can be used to reset the buffers sync clocks and then synchronize the devices. Once they are synched, the only differences between devices will be a slight jitter of no more than ½ a sample period.