Connecting SIMATIC TP177A to CPU313C-2DP via PROFIBUS DP

Overview

The SIMATIC TP 177A (article number 6AV6642-0AA11-0AX1) is a 5.7" blue-mode STN touch panel designed as the successor of the TP170A family. It exposes a single combined MPI / PROFIBUS DP / PPI physical port on the underside of the unit, which is one of the most common sources of confusion during commissioning: the same 9-pin D-sub connector can be re-tasked between MPI and DP depending on what the project download and the panel transfer settings request. The connector body itself is labeled DP/MPI/PPI, which is a useful physical reminder during wiring.

On the PLC side, the SIMATIC S7-300 CPU 313C-2DP (typical MLFBs 6ES7313-6CF03-0AB0, 6ES7313-6CG04-0AB0) carries two PROFIBUS-capable interfaces:

• X1 – combined MPI / DP master or DP slave (default MPI)
• X2 – dedicated DP master / DP slave interface

For a TP 177A on PROFIBUS DP you always wire the panel to the X2 connector of the CPU 313C-2DP. Wiring the TP 177A to X1 (the MPI/DP combo port) and expecting DP communication is one of the most common reasons commissioning fails: X1 defaults to MPI protocol and must be re-tasked in STEP 7 HW Config before DP will work, while X2 is a true PROFIBUS DP interface out of the box.

This tutorial documents the working sequence end-to-end: cabling, STEP 7 HW Config, WinCC flexible connection setup, baud-rate matching, and a recovery procedure for the well-known TP 177A "port-lock" fault where the panel will no longer accept a configuration change.

Prerequisites

Before powering the panel, confirm that you have:

• SIMATIC TP 177A 6" (MLFB 6AV6642-0AA11-0AX1) or TP 177A 4" (MLFB 6AV6642-0BA11-0AX1). The transfer interface is the same family.
• S7-300 CPU 313C-2DP with the second (X2) PROFIBUS DP interface available.
• STEP 7 V5.5 + SPx (or STEP 7 V5.4 + SPx) with the TP 177A GSD/ HSP or the WinCC flexible device library installed.
• WinCC flexible 2005 SP1 or later (WinCC flexible 2008 / 2008 SP2 / 2008 SP3 are all valid; TIA Portal WinCC can also target a TP 177A but only with the correct HSP).
• PROFIBUS DP cable (violet, type A, twisted, shielded, impedance 150 Ω). Standard PROFIBUS cable (e.g. 6XV1830-0EH10) is fine; do not substitute a green MPI cable.
• PROFIBUS connectors with switchable terminating resistor (e.g. 6ES7972-0BA12-0XA0) for the panel and the PLC. The terminator on the last device on the segment must be ON; all others OFF.
• 24 V DC power supply (≥ 0.5 A) for the TP 177A on its X80 connector, separate from the S7-300 24 V bus.

Hardware Topology

The minimum working topology is a two-node DP segment:

Terminating resistor ON at the X2 connector on the CPU and ON at the TP 177A end-connector. Every node in between must have the terminator OFF or the bus will collapse.

STEP 7 HW Config – Enable DP on X2

1. Open SIMATIC Manager and open the S7 project containing the CPU 313C-2DP.
2. Double-click Hardware to launch HW Config.
3. Select the CPU 313C-2DP in the rack. The bottom of the screen shows two interface slots: IF1B (X1) and IF1A (X2).
4. Double-click the IF1A (X2) slot or right-click the DP on the CPU symbol to open Properties – DP Interface.
5. Set:
   • Interface: DP master (default, leave as master for a single-panel HMI link).
   • Address: typical 2 (anything except 0/1 used by other masters).
   • Subnet: create a new PROFIBUS subnet PROFIBUS(1).
   • Transmission rate: 1.5 Mbps is the safe default; 12 Mbps is supported but reduces cable length to ~100 m.
6. Click OK to apply.
7. In the catalog (right pane), navigate to PROFIBUS DP > HMI > SIMATIC TP 177A 6". (The 4" variant is at the same branch level.)
8. Drag the TP 177A onto the PROFIBUS(1) subnet. Assign DP address 3 (must not collide with the CPU X2 address 2).
9. Save and compile (Ctrl+S) and download the HW Config to the CPU (target system > Download).

WinCC flexible – Connection & Project Setup

1. Open WinCC flexible 2008 (or whatever version your plant standard calls for). New Project → choose TP 177A 6" color as the device.
2. Open Project > Transfer > Transfer Settings (or the equivalent in earlier WinCC flexible). On the Configuration tab set Connection type = PROFIBUS and the panel-side baud rate to match the PLC (e.g. 1.5 Mbps). Address must match what you assigned in HW Config (3 in this example).
3. Open Communication > Connections and add a new connection:
   • Communication driver: SIMATIC S7 300/400
   • PLC device: S7 300
   • Connection type: PROFIBUS
   • PLC address: 2 (the X2 master address)
   • HMI address: 3
   • Slot: 2 (CPU slot)
   • Rack: 0
4. Click Test. The connection test should report OK if the bus is wired and the baud rate matches.
5. Build the project and start a Transfer. WinCC flexible will push the project to the TP 177A over PROFIBUS. The panel's transfer progress is shown on its screen.

Baud Rate Reference

The single most common cause of the panel staying in Transfer mode or returning a connection failed dialog is baud-rate mismatch. The TP 177A and the CPU 313C-2DP must agree exactly on the line speed, and the segment cable length must be compatible:

Set the rate in two places and nowhere else: HW Config → DP Interface properties → Transmission rate on the CPU X2, and WinCC flexible → Transfer Settings → Baud rate on the TP 177A. Do not enable Automatic baud rate detection on the CPU unless every other node on the segment is also configured to negotiate.

The TP 177A Port-Lock Fault & MPI Recovery

A well-known field issue affects TP 177A panels: after a failed or interrupted download, after a baud-rate change in the project, or after several rapid restarts, the panel will refuse to accept any new transfer or configuration change. The Transfer dialog no longer shows the new connection, and the panel appears "stuck" on a previous project setting. In most field cases the panel will continue to display the running project, but the configuration can no longer be edited through the touch menu.

The recovery path documented by Siemens and confirmed in the field:

1. Disconnect the PROFIBUS cable from the TP 177A.
2. Open Control Panel on the panel (tap the white area during boot) → Transfer → change Connection type to MPI.
3. Save and restart the panel. The TP 177A will boot in MPI mode and the configuration menu becomes accessible again.
4. Switch the Connection type back to PROFIBUS and re-enter the correct baud rate and address.
5. Save, restart, re-attach the PROFIBUS cable, and re-run the transfer from WinCC flexible.

This works because switching the connection type forces the panel to re-initialise its port handshake logic and clear whatever state machine has become inconsistent. The DP / MPI / PPI legend on the connector housing is a useful reminder that all three protocols share the same physical pins (3 = B, 8 = A, 5 = shield/functional earth) — only the line discipline changes.

Commissioning Procedure (End-to-End)

1. Wire the DP segment with terminating resistors ON at the two end nodes (CPU X2 and TP 177A), OFF in between.
2. Power the S7-300 first; confirm that the X2 DP master LED does not show a station failure.
3. Power the TP 177A. It should boot into either the configured project or the Transfer dialog.
4. In WinCC flexible, run Transfer > Transfer > Start. The panel should show Connecting… followed by Receiving….
5. On the panel, open Project > Status / Control and verify the DP connection reads OK with no bus fault counter incrementing.
6. Run a tag test: a flicker bit on the PLC (clock memory byte MB10, bit MB10.0) should be visible on a tag on the panel updating once per second.

Verification Checklist

Troubleshooting Matrix

Notes for Field Engineers

Two operational caveats that show up repeatedly in commissioning reports:

• Power-up sequence. The TP 177A's bootloader occasionally mis-handles a hot-plugged PLC. Power the S7-300, wait for the X2 DP master LED to settle, then power the TP 177A. If you must hot-swap, press and hold the Transfer touchkey for at least 3 seconds after PLC restart to force the panel back into a clean handshake.
• Connector labeling. The physical imprint DP/MPI/PPI on the D-sub housing is not a protocol selector — it is just a reminder that the same pins are reused. The protocol is set in software (HW Config on the PLC side, WinCC flexible / Control Panel on the panel side) and a single panel can be flashed between protocols at any time, although the MPI recovery trick above is the only safe way to break out of a port-lock state.

FAQ