Configuring SFC 14/15 with ABB ACS800 RPBA-01 Profibus

Overview of SFC 14 and SFC 15 on Siemens S7-300 Profibus DP

The system functions SFC 14 (DPRD_DAT - Read Consistent Data of a DP Standard Slave) and SFC 15 (DPWR_DAT - Write Consistent Data of a DP Standard Slave) are the only correct way to exchange process data larger than four bytes with a DP standard slave / PROFINET IO device. They guarantee consistent, gap-free transfer of the entire data record in a single DP cycle, which is critical when reading drive parameters and writing control words on a Profibus DP link such as that between a Siemens CPU 313C-2DP and an ABB ACS800 inverter with an RPBA-01 Profibus adapter.

Without SFC 14/15, only the first four bytes of a DP slave's input/output area are guaranteed consistent. Drive PZD (Process Data) frames routinely exceed four bytes - PPO 1 has 12 bytes, PPO 2 has 20 bytes, and PPO 5 has 4 bytes - so the standard process-image access (L PIB, T PQW) must NOT be used for the entire PZD area.

Reference: Siemens FAQ: Consistent Data with SFC 14/15 (PDF)

Prerequisites and Required Components

Verify that the following hardware and software are on hand before starting configuration:

Understanding the LADDR Parameter (Hexadecimal Logical Address)

LADDR is the most error-prone input to SFC 14 and SFC 15. It is the configured Profibus I/O start address of the slave module, entered as a 16-bit WORD in hexadecimal form with the prefix 16#.

The address is set in HW Config when the DP slave is placed on the Profibus line:

1. Open SIMATIC 300 Station -> double-click the DP master line on the CPU.
2. Insert ABB RPBA-01 from the hardware catalog (PROFIBUS DP -> Additional Field Devices -> Drives -> ABB -> RPBA-01).
3. Select the PPO type (e.g., PPO 2 "4 PKW / 6 PZD").
4. In the properties dialog of the inserted slot, click "Addresses" and read the configured input and output start addresses.

Configuring the RECORD Parameter (ANY Pointer)

The RECORD parameter is an ANY pointer that defines where the read data is placed (SFC 14) or where the write data is taken from (SFC 15). The standard STEP 7 syntax is:

The notation P#DIX30.0 BYTE 12 that appears in some project documentation corresponds to P#DB<n>.DBX30.0 BYTE 12 under standard STEP 7 syntax - the destination is byte 30 of a particular data block, with 12 bytes of consistent data. With PPO 1 (12 bytes total) the entire PKW+PZD area fits in those 12 bytes starting at byte 30 of the destination DB; with PPO 5 (also 12 bytes) only the PKW portion is unused.

PPO Type Selection for ABB ACS800 / RPBA-01

The Parameter Process data Object (PPO) defines the split between the parameter channel (PKW) and process data (PZD):

For typical ACS800 control with speed reference and feedback plus access to a few diagnostic parameters (e.g., P92.03 actual speed, P93.04 motor current, P93.05 DC bus voltage), choose PPO 2. For minimum-bandwidth applications where only start/stop and one speed value are needed, use PPO 3 or PPO 5.

PZD Mapping Inside the ACS800

After PPO type selection, the user maps which ACS800 signals appear in each PZD word. The mapping is performed via ACS800 parameters (51 group for fieldbus) and must match the expected layout in the destination DB on the PLC.

Default Write PZD layout (PLC -> ACS800)

Default Read PZD layout (ACS800 -> PLC)

ABB ACS800 Control Word Encoding

The ACS800 control word is a 16-bit field. Each bit triggers a specific drive command; the drive state machine responds to the combination of bits:

Common control word values used during commissioning and fault recovery:

ABB ACS800 Status Word Decoding

The status word mirrors the drive's operating state back to the PLC:

Sample STL Code for SFC 14 and SFC 15

The following STL excerpt in OB1 (cyclic) reads and writes PZD/PKW consistent data between DB100 (write) / DB101 (read) and the RPBA-01 slave at LADDR 16#100 with PPO 2 (20 bytes):

// ---- SFC 15: WRITE 20 bytes from DB100 to RPBA-01 output area ----
CALL "DPWR_DAT"
  LADDR  := W#16#100          // Logical start address from HW Config
  RECORD := P#DB100.DBX0.0 BYTE 20
  RET_VAL:= MW210             // Error code (see SFC 15 manual)

// ---- SFC 14: READ 20 bytes from RPBA-01 input area into DB101 ----
CALL "DPRD_DAT"
  LADDR  := W#16#100
  RECORD := P#DB101.DBX0.0 BYTE 20
  RET_VAL:= MW212

// ---- Evaluate status bits ----
A     DB101.DBX  0.0          // RDY_ON
=     M 100.0                 // "Drive Ready to Switch On"
A     DB101.DBX  0.3          // TRIPPED
=     M 100.3                 // "Drive Faulted"
A     DB101.DBX  0.8          // AT_SETPOINT
=     M 100.8                 // "Drive at Reference"

// ---- Build control word ----
SET
=     DB100.DBX  2.0          // OFF1
=     DB100.DBX  2.1          // OFF2 inactive
=     DB100.DBX  2.2          // OFF3 inactive
=     DB100.DBX  2.3          // RUN
// Speed reference scaled 0..20000 = 0..50 Hz
L     MW 150                  // Speed setpoint 0..20000
T     DB100.DBW  2

For bit access on the second PZD the offset starts at bit 16 (DBW2), which corresponds to byte index 2 in the same DB - keep word-boundary crossing in mind when the destination DB crosses byte 30 or higher.

RET_VAL Error Codes (SFC 14 / SFC 15)

Diagnostic Indicators and Troubleshooting Matrix

CPU 313C-2DP Specific Notes

• Maximum DP slaves supported: 32 (limited by DP address space 0-127, not CPU resource).
• Maximum cyclic I/O per slave: 244 bytes input + 244 bytes output - well above PPO 2's 20 bytes.
• The integrated analog inputs (AI0..AI3) of the CPU are NOT to be confused with the ACS800 analog feedback - the drive transmits its values only via Profibus PZD.
• If SFC 14/15 trigger OB85 (diagnostics interrupt), download OB82 and OB85; otherwise the CPU will go into STOP with "OB85 not loaded".
• Firmware version V2.6 or later is recommended for ACS800 with PPO 2 communication (improved DP state machine and diagnostic buffer format).
• The DP port (X2) auto-detects baud rate from 9.6 kbps to 12 Mbps; ensure the rotary switches on RPBA-01 are set to a unique node address between 1 and 126.

Communication Topology and Flow

Commissioning Procedure (Verification)

1. Wire RPBA-01 inside the ACS800, set Profibus node address (rotary switch or P51.02), confirm baud rate auto-detect.
2. Set drive parameter 98.02 = FIELDBUS, 98.01 = FIELDBUS; save with P99.05 (Save).
3. In STEP 7 HW Config, install GSD file ABB_0812.GSD, place RPBA-01 on the DP master line, choose PPO 2.
4. Note configured input and output start addresses (e.g., 256 / 256 = 0x100).
5. Create DB100 (write) and DB101 (read), each 20 bytes; define symbolic names (e.g., "ControlWord", "SpeedRef", "StatusWord", "ActualSpeed").
6. Program SFC 14 and SFC 15 calls in OB1 (cyclic) using LADDR = W#16#100 and RECORD = P#DBxxx.DBX0.0 BYTE 20.
7. Download HW Config + OB1 + DB100/101 to the CPU. CPU should remain in RUN with no SF / BF LED.
8. Online -> Monitor DB101.DBW0 (status word) - expect 0x0F31 at idle (RDY_ON | RDY_RUN | RDY_REF | REMOTE bits all set).
9. Write 16#047F to DB100.DBW0 and 16384 to DB100.DBW2 (half-speed reference); monitor actual speed DB101.DBW2 / DB101.DBW4.
10. Trigger a fault (e.g., block motor rotation with overload); verify status word bit 3 (TRIPPED) sets and a 0x047F -> 0x0C7F transition clears it.
11. Disconnect the Profibus cable; verify RET_VAL changes to 16#80B0 / 16#80C2, BF LED lights, and OB82 / OB86 are invoked.
12. Reconnect cable, clear diagnostics (SF / BF should extinguish within one DP cycle), confirm RET_VAL returns to 16#0000.

FAQ