ACS880 PROFIBUS Transparent Mode: Control and Status Words

The first thing to understand about transparent mode is that there is no fixed control word bit layout to memorize.

The information is not hidden. Under ABB Drives or PROFIdrive, the profile defines how the control word, status word, references and actual values are interpreted. Under Transparent 16 or Transparent 32, the FPBA-01 does not impose that interpretation. The configured process data is transferred as-is, and the drive application decides what the values are used for.

So the meaning of a control word bit comes from the drive-side application and its documentation, not from a generic PROFIBUS transparent-mode bit table. That is the whole point of the mode, and it is why transparent-mode advice from forums so often sends people wrong.

It also changes how you commission. Instead of starting from a remembered bit table, start from what the drive actually received. On an ACS880 using FBA A, 06.03 FBA A transparent control word shows the unaltered control word received through the adapter, which separates a PLC or transmission problem from a drive-side interpretation problem.

This article covers the two directions separately, because they do not work the same way.

What the adapter still does

Transparent does not mean the adapter is a wire. It still:

• runs the PROFIBUS DP slave state machine, handles parameterization and configuration
• moves the configured number of words each cycle, per the PPO type set in the PLC
• places the words into the drive’s fieldbus interface at the positions you map
• handles DP-V1 acyclic services

What it stops doing is interpreting. Control word, status word, references and actual values pass through as raw values.

The receive path: PLC to drive

53.01 FBA A data out1 is the first FBA A data-out mapping, assigned automatically according to the selected profile and configuration. That is where the word from the PLC lands.

To see what arrived, read:

• 06.03 FBA A transparent control word — the unaltered control word received through fieldbus adapter A
• 06.04 FBA B transparent control word — the same for adapter B
• 06.05 EFB transparent control word — the same for the embedded fieldbus interface

This is the most useful parameter in a transparent-mode commissioning session. If 06.03 does not change when the PLC writes, the problem is upstream — mapping, telegram size, or the PLC itself — and there is no point examining drive logic yet.

Do not troubleshoot from 06.01 Main control word instead. 06.01 is the drive’s processed control word, after the drive has interpreted what it received. Comparing 06.03 against 06.01 tells you whether the drive understood the word the way you intended. Looking only at 06.01 blurs the line between “the PLC sent the wrong thing” and “the drive interpreted it differently than I assumed.”

A second control word is available if the application needs one — CW2 16bit appears in the data-out selection list for groups 53 and 56.

The transmit path: drive to PLC

This direction is less symmetrical than people expect, and it is where most transparent-mode confusion lives.

52.01 FBA A data in1 is the status word position, set automatically. But what gets placed there in transparent mode is selected by you.

Group 50 carries the transparent source selectors:

Under ABB Drives or PROFIdrive, the adapter builds the status word for you from the drive state. Under transparent, you point it at a source. If you have not set 50.09, do not assume a sensible default is being sent — check it.

Why 06.11 is not enough

06.11 Main status word is the drive’s main status word. It reflects drive state regardless of control source and regardless of which profile is in use.

It should not be assumed to be identical to the status word transmitted to the PLC. In transparent mode the gap is wider still, because the cyclic status data sent through FBA A is determined by the configured fieldbus data mapping and the transparent source selection.

So if the commissioning question is “what status word is being returned through the fieldbus interface,” do not infer the answer from 06.11 alone. Use the FBA A debug parameters to inspect the fieldbus data path instead.

Inspecting the fieldbus data path

For that, use the fieldbus debug parameters. Set 50.12 FBA A debug mode to enable them, then read:

These are displayed as raw 32-bit hex, which is what you want when the question is “did the right bits move.” Adapter B uses the equivalent parameters in group 55.

Treat 50.16 as the drive’s view of the fieldbus data path, not as a packet capture of what physically appeared on the wire. For that you need a bus analyzer.

06.03 and 50.13 are not the same tool

Both show a received control word, but they answer different questions.

06.03 is a transparent-mode parameter. It exists to show the unaltered control word arriving through FBA A, and it is there whenever a transparent profile is selected. It is the first thing to look at when the drive is not responding as expected.

50.13 is part of the fieldbus debug set. It works under any profile, not just transparent, and it needs 50.12 debug mode enabled. Its value is that it sits alongside 50.14 through 50.18, so you can see the whole cyclic exchange — both directions, references and actuals included — in one place.

Use 06.03 for a quick check of the control word. Use the 50.12 set when you need the full picture of the data path.

Debug mode adds processing load, so turn it off after commissioning rather than leaving it enabled on a production drive.

Between the two you can isolate the receive path completely, and 50.09 with 50.16 covers the transmit path. Working the directions separately is faster than staring at both ends of a full loop.

References and actual values

Scaling in transparent mode depends on more than the profile selection, and this catches people.

Reference type matters. Parameter 50.04 FBA A ref1 type sets the reference type, and 50.07 FBA A actual 1 type does the same for the actual value. The behaviour differs:

• Ref type = Transparent → the T16 scale multiplier applies
• Ref type = General → it does not

The T16 multiplier is narrower than it looks. Parameter 51.06 T16 scale acts as a reference multiplier and actual-value divisor, and it is effective only when all three of these hold together:

• Transparent 16 is the selected profile
• the drive is using its native communication profile
• a 16-bit transparent Reference 1 / Actual value 1 is in use

When it does apply, the reference is multiplied by (51.06 + 1). Default 51.06 is 99, so the multiplier is 100: send 1000 and the drive sees 100000.

Base scaling is drive-family specific. On ACS880 and ACS580, the transparent-mode Reference 1 base scale is 100 = 1, though what that represents depends on the drive application. On ACSM1, ACS850 and ACQ810 the speed scale is roughly 65535 = 1 rpm — a completely different figure.

This is the reason transparent-mode numbers from a forum post about an ACS850 will not work on an ACS880. Check the family before you copy a value.

Transparent 32 differences

Selecting Transparent 32 changes the defaults in groups 52 and 53. Instead of CW 16bit and SW 16bit, the control and status word positions default to CW 32bit and SW 32bit.

The reference and actual selections have 32-bit equivalents in the same lists — Ref1 32bit, Ref2 32bit, and so on.

Two practical consequences:

• Each 32-bit signal consumes two 16-bit process data words instead of one. Whether that requires a different telegram depends on how much process data you are moving — check the configured length against the PPO type you planned, rather than assuming you must step up.
• Data consistency matters more. A 32-bit value read as two separate words can be caught mid-update. That is a PLC-side consideration rather than something PROFIBUS or the adapter imposes: on Siemens S7 systems, SFC14 (DPRD_DAT) and SFC15 (DPWR_DAT) may be required for consistent transfer of larger or structured cyclic data areas, depending on the CPU and configuration.

Commissioning sequence

Order matters here more than in the standard profiles, because nothing is set up for you.

1. Set the profile. 51.05 = 2 (Trans16) or 3 (Trans32) on an FPBA-01. Adapter B uses 54.05.
2. Set the reference and actual types. 50.04 and 50.07, deliberately. Transparent or General changes the scaling behaviour.
3. Set the transparent sources. 50.09 for the status word, 50.10 and 50.11 for actual values. Do not leave these unexamined.
4. Set T16 scale. 51.06, if Transparent 16 and a transparent Reference 1 are both in use.
5. Map the process data. Groups 52 and 53 from index 02 onward. Index 01 in each is set automatically.
6. Save, then refresh. 96.07 Parameter save manually, then 51.27 FBA A par refresh = Refresh. 51.27 cannot be changed while the drive runs.
7. Verify the receive path. Read 06.03 while the PLC writes. The value should track.
8. Verify the transmit path. Enable 50.12 debug mode, read 50.16, compare against what the PLC displays.
9. Turn debug mode off before handover.

When transparent mode is the wrong choice

Worth saying plainly, because the mode attracts people who do not need it.

Transparent means you own the interface. The adapter does not impose a standard bit layout, so there is no profile document a future engineer can look up — the meaning lives in your drive application program and whatever documentation you write yourself.

That does not mean the drive stops reporting its state. 06.11 and the drive status words are still there, and the fieldbus comm-loss function still works. What you give up is the adapter automatically assembling a profile status word, with named bits like FBA_ERROR, into the cyclic data. If you want that information in the telegram, you map it yourself.

That is a fair trade when you are running a drive application program with a custom control word layout, or you need process data the standard profiles do not expose. It is a poor trade when ABB Drives would have worked and someone simply wanted “raw access.”

If you are choosing transparent because a standard profile scaled a reference in a way you did not expect, fix the scaling instead. That problem is a parameter, not a profile.

FAQ