PROFIBUS MC

The difference between PROFIBUS MC and PROFIBUS DP is that the PROFIBUS cycle is constant, with a jitter of a few microseconds (for PROFIBUS DP, the jitter is greater than 100µs), and at the start of the cycle a broadcast global control telegram is sent, which can be used by the MC slaves for synchronization. This enables precise synchronization of drive control loops with the NC.

However, this precise synchronization means that bus disturbances, switching off of slaves, pulling of bus plugs etc. will usually lead to a loss of synchronicity between master and slave, since the bus timing is changed.

FC310x with Simodrive 611U has Plug&Play functionality

The following steps are required for operating a Simodrive 611U on a FC310x:

1. Set FC310x to operating mode ”DP/MC (equidistant)”.
2. Add box ”Siemens AG, Profidrive MC”.
3. Adjust 611U station address (”PROFIBUS” box tab).
4. Append axis (or 2 axes for 611U with 2 axes) to NC task, select axis type ”continuous axis”.
5. Link axis (or axes) with 611U (select axis type ”ProfiDrive MC” in the ”Settings” axis tab, then link with 611U; for a 2-axis 611U, both axes have to be linked, otherwise a 611U error will occur).
6. Press the ”Calculate equi-time” button on the ”FC310x” tab at the FC310x.
7. Save project in the registry and start TwinCAT. The 611U should now change to RUN, the axis can be operated via the NC online menu.

Should this not be the case, check the following:

• DpState of the 611U in TwinCAT is 2: Check 611U station address.
• DpState of the 611U in TwinCAT is 5: Check whether the correct PROFIBUS module is inserted at the 611U.
• DpState of the 611U in TwinCAT is 7: Check whether P922 is set to the correct standard telegram (according to the ProcessData tab for 611U in the System Manager).
• DpState of the 611U in TwinCAT is 0, but 611U still does not change to RUN: Check the 611U firmware version; for firmware versions below 3.4.3, 611U synchronization errors (error 597 or 598) can only be rectified via a hardware reset of the 611Us, otherwise look up the error code in the Siemens manual.

If several 611Us are configured, the equidistant times may have to be adjusted (see below).

DP/MC Equidistant Mode

In order to operate the FC310x with PROFIBUS MC it is necessary to set the "DP/MC (Equidistant)" Operation Mode on the master's "FC310x" tab (for TwinCAT 2.8 and TwinCAT 2.9). Whichever task uses the equidistant functionality of the FC310x (most often this is the NC task) should have the highest priority, as otherwise the synchronicity can be disturbed. Additionally, the Sync Mode can be selected. This specifies where the synchronization signal is generated.

Disabled (PC is Sync Master)

The synchronization signal is generated by the PC, the FC310x synchronizes itself with the PC (PROFIBUS cycle jitter approx. 2-4 µs).

The NC Access Time specifies by how much the PROFIBUS cycle is shifted towards the TwinCAT cycle, the PLL Sync Time should be set to approx. 10% of the NC-Access-Time (max. 50 µs).

Sync Slave

The synchronization signal comes from another device, whose Sync mode must be set to ”Sync Master”. The connection between the sync master and the sync slave is made through a hardware link. This is only supported as from FC310x hardware version 4 and firmware version 3.00. No times have to be set.

Sync Master

The synchronization signal is generated by the FC310x, the PC synchronizes itself with the FC310x (jitter of the PROFIBUS cycle approx. 1 µs).

The NC Access Time specifies by how much the TwinCAT cycle is shifted towards the PROFIBUS cycle.

Setting of Equidistant Times

The Calculate Equi Times button (TwinCAT 2.8: see master's  FC310x tab,  TwinCAT 2.9: see master's MC tab) can be used to set all the equidistant parameters automatically. The only parameter that may possibly have to be adjusted later is the NC Access Time, because this depends on the maximum TwinCAT jitter and on the maximum mapping time. This in turn depends on all the devices, so that adding and linking boxes to other devices has the effect that it may nevertheless be necessary to change the NC Access Time for an unchanged device. If "I/O not at task start" is selected (see the Synchronization section), then the NC Access Time also depends on the task runtime. In order to avoid the NC Access Time having to be adjusted manually every time the Calculate Equi-Times button is pressed, the ratio of NC Access Time to Cycle Time can be specified (default is 15%).

Disabled (PC is Sync Master) or Sync Master

The NC Access Time must be greater than the maximum TwinCAT jitter plus the maximum mapping time, plus, if "I/O not at task start" is selected for whichever task linked to the FC310x has the highest priority, it's task runtime.

Diagnosis of Equidistant Times

Diagnostics of the equidistant times can be carried out with the EquiDiag tab (TwinCAT 2.8) or MC-Diag (TwinCAT 2.9) in the System Manager, of by ADS in the controller program (see Master Diagnostics section).