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Knowledge Base: Input

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Q10103 Configuring DAP boards for master/slave clocking

Tags: Help, synchronization, configuration, sampling, master/slave, multi-DAP

Applies to: DAP and iDSC board families using synchronization cables

I have multiple DAP boards connected with synchronization cables. Do I need to do anything special to operate these boards?

You need some special things — special, but not difficult to do or difficult to understand. First, makes sure that the synchronization cable is correctly installed (see the references for more information about synchronization cables). The master end of the cable must connect to the DAP board that is to act as the master.

For the software configuration, you need to designate which board acts as the master board. The master board is the one that will send the hardware timing signals through the synchronization connector to coordinate the other boards. To do this, simply include an extra MASTER command in the sampling configuration you send to the master. For example:

  // MASTER - DAP 0
  idefine  master_sampler
    channels 4
    set ip0  s0
    set ip1  s1  40
    set ip2  s2  40
    set ip3  s3  40
    time  5.00

You also need to designate all of the DAP board that are connected as slave boards. The slave boards will ignore the hardware timing signals generated on-board or by external triggering and clocking pins, and will instead wait for the timing signals to arrive from the master through the synchronization connector. To configure this, simply include an extra SLAVE command in the sampling configuration for each slave board. For example, a corresponding slave configuration:

  // SLAVE 1 of 2 - DAP 1
  idefine  slave_sampler
    channels 4
    set ip0  s0
    set ip1  s1
    set ip2  s2
    set ip3  s3
    time  5.00

Some important details about the slave configuration:

  • Even though the slave does not use the on-board hardware signals implied by the sampling time interval of 5 microseconds, you must specify this anyway. It allows the DAPL system to configure buffer storage and some of its internal timing correctly.

  • DAP models like DAP5400a or DAP5380a that sample multiple input signals simultaneously can also serve as a master or slave, acting in the same manner except that each sampling operation captures a pin group.

  • There are no hardware triggering or external clocking modes here. All external timing goes to the master, with slaves responding only to timing signals from the master.

  • The slave configurations are started immediately. The master configuration is not.

The reason for starting all of the slaves first is that they must be ready and running at the time that the master generates the first timing pulse, otherwise the slaves cannot respond to the master and synchronization is lost. When started, the slaves will do everything they need to do to prepare for sampling, then wait at the point where their hardware needs the first sampling pulse. You can be sure that the slaves are ready in one of two ways:

  1. Configure all of the boards and then send the master board a separate START command.

  2. Put a START command at the end of every configuration file, but make sure that the master board receives its configuration last.

For maximum reliability in the startup sequence, insert a time delay (perhaps 1/2 second to 1 second) between starting the last slave and starting the master.

At the end of the sampling activity, reverse the start-up order — send a STOP command to the master first, then stop all of the slaves. That way, the slave boards will stop in an orderly manner when the master board stops sending sample pulses.


Knowledge base article Q10102 discusses the hardware synchronization cables that you must use with board operated in a master/slave configuration.

The DAPL 3000 manual discusses master/slave considerations when using software triggering.