TP170A RS232 Communication: Cable Wiring and Program Transfer

Overview: Why the TP170A Will Not Talk to Your Laptop

The SIMATIC TP170A is a 5.7-inch operator panel from the Siemens TP170 family. Unlike its successor TP170B, the TP170A does not have an integrated Ethernet or USB configuration port. The only practical paths for moving a configuration PC ↔ TP170A in the field are the serial RS232 channel on the panel's underside and the MPI/PROFIBUS-DP port. The vast majority of "the cable does not work" incidents reported on TP170A projects come from three root causes:

1. Using the MPI/DP cable (6ES7901-0BF00-0AA0) instead of the RS232 cable (6ES7901-1BF00-0AA0). The two part numbers differ by a single digit but are not interchangeable for project transfer.
2. Connecting a USB-to-serial dongle in place of a true PC COM port. WinCC flexible 2005 and ProSave do not enumerate most generic USB-RS232 converters reliably on the TP170A transfer protocol.
3. Attempting to read back the project from the panel with WinCC flexible. Only a one-way download is supported; reading/editing requires ProSave and a compressed backup file (.brf / .crc pair), not a recompilable WinCC flexible source.

This reference covers the correct cable, the pin assignment, the gender-changer caveat, the ProSave backup/restore flow, and how the same panel integrates with a SIMATIC S7-300 CPU315 over MPI.

Prerequisites

Cable Selection: 6ES7901-0BF00-0AA0 vs 6ES7901-1BF00-0AA0

Siemens sells two visually similar 3 m PC-PP cables that are easy to confuse. The difference is a single character in the order number and the entire signal meaning.

RS232 Cable 6ES7901-1BF00-0AA0 Pin Assignment

The cable is a null-modem style crossover with handshaking. The TP170A is configured as DCE on its underside DE-9 female port, so the cable is the crossover variant. The factory cable ships with two female DE-9 connectors and the following internal wiring (identical on both ends):

If you build the cable yourself, the minimum viable wiring is 2 ↔ 3, 4 ↔ 6 (each end), 5 ↔ 5, 7 ↔ 8. Pins 1 and 9 may be left open. Use shielded cable; the shield is bonded to the DE-9 metal shell on both ends. Total length should not exceed 15 m for reliable transfers, although Siemens rates the part at 3 m / 5 m / 10 m variants.

Connecting the TP170A to a PC COM Port

1. Power the TP170A. The unit must complete its boot cycle to the configuration menu (it will display "Connect to host..." or enter transfer mode automatically on first power-up with no project).
2. On the TP170A, enter Control Panel → Transfer and confirm that the channel is set to Serial, baud 9600, even parity, 8 data bits, 1 stop bit (these are the TP170A factory defaults; do not change them for project transfer).
3. Plug the female DE-9 end of 6ES7901-1BF00-0AA0 into the TP170A's underside serial port.
4. Plug the other female DE-9 into the PC's COM1 (or COM2). The PC end requires a gender changer (DE-9 male/male) if your PC cable is terminated male, OR a short male-to-female serial extension if your PC port is male. Most desktop PCs ship with a male DE-9 COM port, so a standard male-male gender changer is the most common field fix.
5. Verify the COM port number in Windows Device Manager → Ports (COM & LPT). Note the COM number — you will need it in WinCC flexible.

Transferring the Project with WinCC flexible 2005

1. Open WinCC flexible 2005 SP2 (or later). Open the TP170A project (.hmi) and select Project → Transfer → Transfer (Ctrl+Shift+Alt+F5 in the classic UI).
2. Choose Serial as the mode. The default target is the PC's COM1; change it to the COM port you noted earlier.
3. Tick "Overwrite existing project" if you are replacing a working program. The TP170A will not refuse the new project; the old one is overwritten in place. The system files (firmware, OS image) are left untouched.
4. Click Transfer. The progress bar should begin advancing within 3 s. A 256 KB project typically completes in 40-90 s at 9600 baud; a fully populated 1 MB project can take 6-8 min.
5. The TP170A will restart automatically once the new project has been written and verified.

Backup and Restore with ProSave

WinCC flexible can only download to the TP170A. To make an editable archive you must use ProSave, which is installed alongside WinCC flexible (Start → Siemens Automation → SIMATIC → ProSave).

1. Launch ProSave. From the General tab select Device type: TP170A and Connection: Serial. Set the COM port.
2. Click Backup. ProSave creates two files on the PC: <panelname>.brf (compressed image, contains runtime, project, recipes, passwords) and <panelname>.crc (checksum). Both must be kept together.
3. To restore, choose Restore, point at the .brf file, and click Transfer. The TP170A is restored exactly to the backed-up state, including any panel-side passwords.
4. The .brf archive is not editable. You cannot open it in WinCC flexible, change a screen, and recompile. Restoration is intended for disaster recovery on the same TP170A model only — restoring a TP170A backup onto a TP170B or TP170micro will fail the device-type check.

Connecting the TP170A to a SIMATIC S7-300 CPU315 over MPI

For the online link (panel → PLC), use the MPI cable 6ES7901-0BF00-0AA0 (or the pre-assembled 6ES7 705-0AA00-7BA0 PROFIBUS cable with integrated PG socket). The two ends differ from the RS232 cable:

• Cable 6ES7901-0BF00-0AA0 has two male DE-9 connectors. The TP170A MPI port is female, and the CPU315 MPI port is also female — so the cable plugs straight in on both sides with no gender changer.
• The cable cannot be used to connect a CPU315 to a SIMATIC OP3 in the same wiring path (OP3 uses a different pinout on its programming port). A dedicated OP3 cable is required for that scenario.
• Default MPI address: TP170A = 1, CPU315 = 2. Verify in STEP7 → Set PG/PC Interface → MPI and in WinCC flexible → Connections → S7-300 MPI.

If you have a PROFIBUS DP connector with a PG socket (6ES7972-0BB12-0XA0) on the CPU end, simply unplug the PG cable from the panel and re-route the bus through the connector — no re-wiring is needed; the bus is just daisy-chained.

Verification Checklist

Troubleshooting Matrix

Cable Build Notes and Field Practice

When you must build the RS232 cable yourself, three rules keep it working the first time:

1. Cross 2 ↔ 3, cross 4 ↔ 6, cross 7 ↔ 8, and tie 5 to 5. Pins 1 and 9 are unused. Do not wire them to anything; a stray jumper on pin 1 is enough to confuse the TP170A's DCD sense logic.
2. Loop 4 ↔ 6 and 7 ↔ 8 on each end of the cable (DTR-DSR and RTS-CTS local handshakes) — this is a true null-modem with full handshaking, not a three-wire cable.
3. Bond the shield to the metal shell of both DE-9 hoods. The shield is the only return path for high-frequency noise on a 10 m run next to a VFD or motor contactor.

Mark the cable clearly with a label or heat-shrink tag reading "RS232 — TP170A ↔ PC" to prevent the next shift from grabbing it for an MPI job. Most broken projects in the field are traced to a mis-cabled MPI cable, not a defective TP170A.

When to Upgrade Off the TP170A

The TP170A was made obsolete by Siemens in the early 2010s. It uses a custom Windows CE image, the last WinCC flexible revision that targets it cleanly is WinCC flexible 2008 SP2. If you are starting a new project, choose the TP700 Comfort, KTP700, or KTP1200 Basic instead — they are Ethernet-native, support TIA Portal, and are still in production. The TP170A remains in service largely in legacy S7-300 cells where the cost of re-engineering a screen outweighs the benefit of TIA Portal integration.