Siemens TP177B Color PN/DP to Allen-Bradley SLC 5/04 over DF1 Full Duplex
The Siemens SIMATIC TP177B 4" Color PN/DP (catalog number 6AV6642-0BD01-3AX0) is a 5.7-inch STN color touch panel with both PROFINET and PROFIBUS DP interfaces, plus a serial sub-D interface that supports RS422/RS485. The Allen-Bradley SLC 5/04 processor exposes Channel 0 (CH0) as an RS-232 port running DF1 Full Duplex. Because the electrical layers differ (RS422/RS485 on the HMI side, RS-232 on the PLC side), a hardware adapter is mandatory, and the protocol must be DF1 Full Duplex — not DH-485. This reference walks through a field-proven commissioning sequence including dip-switch setup on the panel, the RS422-to-RS232 adapter (Siemens 6AV6671-8XE00-0AX0), the null-modem cable, CH0 channel configuration in RSLogix 500, and the WinCC Flexible 2008 connection parameters that finally bring up the link.
Reference product documentation: Siemens TP177B 4" PN/DP Color product support page and the SIMATIC TP 177B / OP 177B delivery release note.
1. System Architecture and Signal Path
The communication path is a three-segment serial chain:
The TP177B's IF1B sub-D port is wired as RS422 differential; the SLC 5/04's CH0 DB-9 is wired as RS232 single-ended. The 6AV6671-8XE00-0AX0 adapter performs only electrical level translation — no protocol conversion. The WinCC Flexible "Allen-Bradley SLC500" driver encapsulates DF1 frames for the SLC 5/04 to decode.
2. Prerequisites
2.1 Hardware
| Item | Catalog / Part | Notes |
|---|---|---|
| SIMATIC TP177B 4" Color PN/DP | 6AV6642-0BD01-3AX0 | Blue Mode / WinCC Flexible 2008 runtime image |
| RS422/RS232 converter | 6AV6671-8XE00-0AX0 | Plugs directly into TP177B sub-D; do not substitute generic USB-serial |
| Null-modem cable (DB-9 F/F) | AB 1747-CP3 or equivalent | Tx/Rx crossed, no handshaking required |
| SLC 5/04 processor | 1747-L541, L542, L543, or L544 | DF1 Full Duplex on CH0 |
| Configuration PC | RSLogix 500 v7.x or later | For CH0 channel setup |
| HMI engineering PC | WinCC Flexible 2008 SP1 or later | Includes "Allen-Bradley SLC500" driver |
2.2 Firmware and Image Versions
TP177B must run a WinCC Flexible image that supports the SLC500 driver. The earliest compatible image is the WinCC Flexible 2004 SP1 release; WinCC Flexible 2008 SP2 and SP3 are recommended for stability. The PROFIBUS DP interface on the panel supports up to 12 Mbit/s per the TP177B delivery release note, but the IF1B serial port used for DF1 is limited to 187.5 kbit/s — and in practice, 19200 bit/s is the highest reliable rate to an SLC 5/04.
3. TP177B IF1B Port and Dip-Switch Setup
The TP177B exposes its IF1B port as a 9-pin sub-D on the rear of the unit. The port can be configured for RS422, RS485, or MPI/DP via an 8-position DIP switch bank on the rear of the panel. For DF1 to an SLC 5/04, the port MUST be switched to RS422.
3.1 Dip Switch Positions (IF1B → RS422)
| Switch | Position | Function |
|---|---|---|
| S1 | OFF | Termination off (panel is end-of-segment in a 2-node link) |
| S2 | OFF | No transmit bias to ground |
| S3 | OFF | RS422 mode (not RS485) |
| S4 | OFF | Transmit enable controlled by driver, always on for RS422 |
| S5 | ON | IF1B is RS422 (the alternative ON/ON/ON/ON selects MPI/DP; for RS422 set per Siemens manual table) |
| S6 | OFF | Reserved / no function on TP177B |
| S7 | OFF | Reserved |
| S8 | OFF | Reserved |
3.2 IF1B Sub-D Pinout (RS422 mode)
| Pin | Signal | Direction | Notes |
|---|---|---|---|
| 1 | TX+ | OUT | Differential transmit, positive |
| 2 | TX- | OUT | Differential transmit, negative |
| 3 | RX+ | IN | Differential receive, positive |
| 4 | nc | — | Not connected in RS422 mode |
| 5 | GND | — | Signal ground |
| 6 | nc | — | Not connected |
| 7 | nc | — | Not connected |
| 8 | RX- | IN | Differential receive, negative |
| 9 | nc | — | Not connected |
4. RS422/RS232 Adapter (6AV6671-8XE00-0AX0)
The Siemens 6AV6671-8XE00-0AX0 is a passive RS422/RS485 → RS232 level translator that plugs directly into the TP177B IF1B sub-D and presents a DB-9 female on its output side for the null-modem cable to the SLC 5/04. Internal conversion is performed by a Maxim MAX3467-class transceiver; no external power is required. The adapter is wired to convert the four-wire differential signals (TX+/-, RX+/-) to the three-wire RS-232 signals (TXD, RXD, GND) used by the SLC 5/04 CH0.
Field-proven alternatives include third-party industrial converters (e.g., B&B Electronics 232CL9R or Phoenix Contact PSI-REP-RS422). A generic USB-RS232 cable such as the FTDI USB-COMi-PL will NOT work because it does not perform the RS422→RS232 electrical conversion; the TP177B's differential signaling has no return path back to the FTDI chip.
4.1 Null-Modem Cable Wiring (1747-CP3 Equivalent)
The 1747-CP3 is a 9-pin female-to-female null-modem cable with the following internal connections (DF1 Full Duplex uses no handshaking):
| Adapter end (DB-9 F) | Signal | SLC 5/04 CH0 end (DB-9 F) | Signal |
|---|---|---|---|
| Pin 2 | TXD (from adapter output) | Pin 3 | RXD (to PLC) |
| Pin 3 | RXD (from adapter output) | Pin 2 | TXD (from PLC) |
| Pin 5 | GND | Pin 5 | GND |
| Pin 7 | RTS | Pin 8 | CTS |
| Pin 8 | CTS | Pin 7 | RTS |
| Pin 4 | DTR | Pin 6 | DSR |
| Pin 6 | DSR | Pin 4 | DTR |
5. SLC 5/04 Channel 0 Configuration (RSLogix 500)
Open the SLC 5/04 project in RSLogix 500, double-click the Channel Configuration entry in the project tree, and configure CH0 as follows:
| Parameter | Setting | Notes |
|---|---|---|
| Driver | DF1 Full Duplex | Required — not DF1 Half Duplex, not DH-485 |
| Baud | 19200 | Highest reliable rate for TP177B ↔ SLC 5/04 over RS422↔RS232 |
| Parity | None | Must match WinCC Flexible setting |
| Stop Bits | 1 | Must match WinCC Flexible setting |
| Source ID | 0 | Decimal node number of the SLC 5/04 |
| Control Line | No Handshaking | DF1 Full Duplex does not require RTS/CTS |
| Error Detection | BCC | Block Check Character, must match WinCC Flexible |
| Embedded Responses | Auto Detect (with duplicate-packet detect) | Lets the SLC pick the most efficient framing |
| ACK Timeout (×20 ms) | 50 | 1.0 second total — sufficient for serial polling |
| NAK Retries | 3 | Match WinCC Flexible poll behavior |
| ENQ Retries | 3 | Match WinCC Flexible poll behavior |
5.1 Working RSLogix 500 Channel 0 Screenshot Description
- Open Controller Properties → Channel Configuration → Channel 0.
- Click Driver and select DF1 Full Duplex from the dropdown.
- Set Baud Rate to 19200.
- Set Parity to None, Stop Bits to 1.
- Set Source ID to 0 (decimal).
- Set Control Line to "No Handshaking".
- Set Error Detection to BCC.
- Set Embedded Responses to "Auto Detect" and tick "Duplicate Packet Detect".
- Leave ACK Timeout at 50 (×20 ms = 1000 ms).
- Set NAK Retries and ENQ Retries to 3.
- Download to the SLC 5/04 and place the processor in RUN mode.
6. WinCC Flexible 2008 Connection Configuration
Open the WinCC Flexible project, select Project → Communication → Connections, and add a new connection. The following parameters produce a stable link to the SLC 5/04:
| Parameter | Value |
|---|---|
| Interface | IF1B |
| Type | RS422 |
| Baud rate | 19200 |
| Data bits | 8 |
| Parity | None |
| Stop bits | 1 |
| Checksum | BCC |
| CPU Type | SLC50X |
| Destination Address (decimal) | 0 |
6.1 Step-by-Step in WinCC Flexible 2008
- In the project tree, right-click Connections and choose Add Connection.
- Name the connection (e.g.,
SLC504_DF1). - Set Communication Driver to Allen-Bradley SLC500 (this driver is the one that speaks DF1 Full Duplex to SLC 5/03/04/05 processors).
- Set HMI Device to TP177B Color PN/DP.
- Set Interface to IF1B, Type to RS422.
- Set Baud rate to 19200, Data bits to 8, Parity to None, Stop bits to 1.
- Set Checksum to BCC. CRC is not supported by the SLC 5/04.
- Set CPU Type to SLC50X (covers 5/03, 5/04, 5/05).
- Set Destination Address to 0 (matches the Source ID in the SLC).
- Compile and download the project to the TP177B over Ethernet (PROFINET) — do not use IF1B for project transfer; the serial port is for runtime polling only.
7. Tag Mapping Reference
The WinCC Flexible Allen-Bradley SLC500 driver uses symbolic address notation. The following examples cover the most common SLC 5/04 data files:
| SLC File | PLC Address | WinCC Flexible Syntax | Data Type |
|---|---|---|---|
| Input | I:1/0 | I:1/0 |
BOOL |
| Output | O:2/5 | O:2/5 |
BOOL |
| Integer | N7:0 | N7:0 |
INT (16-bit) |
| Float | F8:0 | F8:0 |
REAL (32-bit IEEE 754) |
| Timer | T4:0.ACC | T4:0.ACC |
INT (preset/accumulator) |
| Counter | C5:0.ACC | C5:0.ACC |
INT |
| Binary | B3:0/0 | B3:0/0 |
BOOL |
| Long Integer | L9:0 | L9:0 |
DINT (32-bit) |
8. Commissioning and Verification
- Power down the TP177B and SLC 5/04.
- Verify all dip switches on the TP177B rear are in the RS422 position.
- Plug the 6AV6671-8XE00-0AX0 adapter firmly into the TP177B IF1B sub-D and tighten the screws.
- Connect the 1747-CP3 null-modem cable between the adapter and the SLC 5/04 CH0.
- Power the SLC 5/04, verify CH0 mode LED indicates DF1 Full Duplex.
- Power the TP177B, allow the WinCC Flexible image to boot.
- Open Control Panel → Transfer → confirm IF1B is set to RS422.
- Open Control Panel → OP Diagnostics → Status (if available). Verify the IF1B status reads "OK".
- Trigger a tag read: navigate to a screen with a numeric I/O field bound to
N7:0; the field should display the live value from the SLC. - Use the SLC 5/04's CH0 LEDs: TX/RX activity should flicker at the configured poll rate.
8.1 Verification Checklist
| Check | Expected Result |
|---|---|
| TP177B IF1B dip switch | RS422 position confirmed |
| Adapter model | Siemens 6AV6671-8XE00-0AX0 seated firmly |
| Null-modem cable | 1747-CP3 or equivalent, DB-9 F/F |
| SLC CH0 driver | DF1 Full Duplex, 19200, 8/N/1, BCC, No Handshaking |
| SLC CH0 Source ID | 0 (decimal) |
| WinCC Flexible connection | IF1B, RS422, 19200, 8/N/1, BCC, SLC50X, Dest=0 |
| Tag read test | Live value updates every poll cycle |
| CH0 LED activity | TX and RX flicker symmetrically |
9. Troubleshooting Matrix
| Symptom | Likely Root Cause | Corrective Action |
|---|---|---|
| No communication, all LEDs dark | Wrong dip-switch position on TP177B | Set IF1B to RS422 per silk-screen |
| No communication, SLC CH0 TX LED on but no RX | Cable wiring — TX not crossing to RX | Verify null-modem; pins 2↔3, 5↔5 |
| Intermittent communication, drops at 19200 | Baud too high for noise environment | Drop to 9600 on both ends |
| PLC error S:5/0 (major) set after download | Baud mismatch between SLC CH0 and WinCC | Match 19200/9600 on both sides |
| Runtime shows connection OK but tags return 0 | Source ID / Destination Address mismatch | Set SLC Source ID = WinCC Destination = 0 |
| WinCC Flexible compile error "CRC not supported" | Checksum set to CRC instead of BCC | Change to BCC in the connection |
| Panel boots, IF1B option grayed out | Wrong WinCC Flexible image loaded | Reload image with SLC500 driver |
| All tag reads show "####" or invalid | Wrong CPU type selected | Set CPU Type to SLC50X (covers 5/04) |
| Communication OK at 9600 only | Adapter or cable too long, capacitance issue | Shorten cable; verify shield grounded at one end |
| WinCC Flexible transfer fails | IF1B being used for project download | Transfer over Ethernet (PN); reserve IF1B for runtime |
| SLC S:5/11 (DH-485 active) set | DH-485 attempted in error | Switch back to DF1 Full Duplex in CH0 config |
10. Common Field Pitfalls
10.1 Using DH-485 Instead of DF1
DH-485 is an RS-485 half-duplex multi-drop protocol. The SLC 5/04 only supports DH-485 on CH1 (or via an external 1761-NET-AIC on CH0). The TP177B's IF1B port can be set to RS485, but it cannot interop with DH-485 framing because the TP177B has no DH-485 driver in WinCC Flexible. Trying to "make DH-485 work" by setting IF1B to RS485 will fail at the first poll cycle.
10.2 USB-Serial Cable Instead of the Siemens Adapter
A USB-to-RS232 cable (e.g., FTDI USB-COMi-PL) provides only single-ended RS-232 levels. The TP177B IF1B port outputs differential RS422 levels. Without the 6AV6671-8XE00-0AX0 converter, the differential pair has no common-mode reference for the RS-232 receiver and the link will fail silently — no error, just no data.
10.3 Using RS485 Instead of RS422 on TP177B
RS485 half-duplex toggles the direction of the differential pair using a DE/RE pin. RS422 is full-duplex with separate transmit and receive pairs. DF1 Full Duplex requires full-duplex operation. If IF1B is set to RS485, the TP177B can only transmit or receive at any given instant and the SLC 5/04 will repeatedly NAK the HMI polls.
10.4 Baud Rate Too High
Although both the TP177B and the SLC 5/04 advertise 19200, the combination of the passive adapter, a marginal null-modem cable, and industrial noise often produces errors at 19200 in the field. The pragmatic first configuration is 9600. Only step up to 19200 after verifying 10 minutes of stable polling with no NAK retries recorded.
10.5 Wrong Source / Destination Address
The SLC 5/04 CH0 Source ID must equal the WinCC Flexible Destination Address. Both are decimal node numbers. Source ID = 0 means the SLC is node 0; WinCC Destination = 0 means the HMI is talking to node 0. They must agree. A mismatch produces no error at startup, but every poll is ignored.
11. Performance and Throughput Notes
DF1 Full Duplex over a 19200 bit/s link provides approximately 1.9 KB/s of raw bandwidth, of which about 80% is available for application data after DF1 framing overhead. With WinCC Flexible's default polling strategy (every 250 ms per tag), a screen with 50 tags generates roughly 200 polls/second of aggregate demand. This is well within the capacity of DF1 Full Duplex at 19200. If tag count exceeds 200 or poll intervals are forced below 100 ms, drop baud to 9600 and/or use the embedded-response feature (already enabled by default on the SLC).
11.1 Recommended Poll Configuration
| Tag Count | Recommended Baud | Recommended Cycle |
|---|---|---|
| < 50 | 19200 | 250 ms |
| 50–150 | 19200 | 500 ms |
| 150–300 | 9600 | 500 ms |
| > 300 | 9600 | 1 s |
12. Reference Topology Diagram (State Machine)
13. Documentation References
- Siemens TP177B 4" PN/DP Color product support — part number, image downloads, manuals.
- TP 177B / OP 177B delivery release note — DP bus speed, image version compatibility.
- Allen-Bradley SLC 500 Instruction Set Reference Manual (1747-RM001) — DF1 framing details.
- Allen-Bradley DF1 Protocol and Command Set Reference Manual (1770-6.5.16) — full-duplex handshake rules.
Can I use DH-485 between a Siemens TP177B and an SLC 5/04?
No. DH-485 is RS-485 half-duplex and the TP177B has no DH-485 driver in WinCC Flexible. Configure the SLC 5/04 CH0 for DF1 Full Duplex and use the Siemens 6AV6671-8XE00-0AX0 RS422-to-RS232 adapter with a null-modem cable (1747-CP3 or equivalent).
Do I really need the Siemens 6AV6671-8XE00-0AX0, or can I use any RS422/RS232 converter?
Any industrial RS422-to-RS232 passive converter that plugs into the TP177B IF1B sub-D and presents a DB-9 will work electrically, but the Siemens adapter is purpose-built for this pinout and requires no external power. A generic USB-to-RS232 cable will NOT work because it does not convert the TP177B's differential RS422 levels to single-ended RS232.
What baud rate should I use first when commissioning?
Start at 9600 bit/s on both the SLC 5/04 CH0 and the WinCC Flexible IF1B connection (8 data bits, no parity, 1 stop bit, BCC checksum, no handshaking). Once you have 10 minutes of stable polling with no NAK retries, step up to 19200 if needed for screen refresh performance.
Why does the WinCC Flexible image only show MPI/PROFIBUS for the IF1B port?
The IF1B port is set by the DIP switch bank on the rear of the TP177B. If the switches are in the MPI/DP position, WinCC Flexible disables the RS422/RS485 options. Power down the panel, change the dip switches to RS422, and reboot — the RS422 option will then appear in the Control Panel and in the WinCC Flexible transfer settings.
Can I program the SLC 5/04 over the same CH0 port the TP177B is using?
Yes, but only if you use "DF1 Full Duplex - Point to Point" in RSLogix 500 and the programming PC is the only DF1 master on the link. If you need simultaneous HMI polling and programming, install an Allen-Bradley 1747-AIC and run DH-485 on a separate channel, or add a second DF1 node with a unique Source ID.