Sinumerik 810T Loading PLC Program When V24 Port Fails

1. Problem Overview

On a Sinumerik 810T-controlled lathe fitted with Siemens NC card 6FX1132-8BB01, operators frequently report a state in which:

• The card powers up, the operator panel responds, and R-parameter input via the machine keypad is accepted.
• Parameter transfer from a PC running PCIN to the same V.24 (RS-232-C) port is rejected or terminates with a timeout.
• Tuning parameters R5010, R5011, R5013, and R5016 – the standard 810T spindle and axis tuning set – can be entered manually but cannot be re-loaded from a backup.
• The machine is otherwise fully operational, but the PLC user program cannot be transferred back after a card swap or battery failure.

The functional question is therefore: can the PLC user program be entered through the operator-panel keypad when the V.24 link is unusable? The short answer is no – the keypad accepts only R-parameters, zero offsets, tool offsets, and settable machine data; the STEP 5 PLC image must always be loaded through a serial interface or an EPROM/ASM module. The remainder of this reference explains the architecture, the diagnostic path, and the three supported loading routes, with emphasis on the often-overlooked second V.24 channel that exists on the 6FX1132-8BB01.

2. Sinumerik 810T System Architecture

The Sinumerik 810T is a lathe-variant member of the Sinumerik 810/820 family introduced in the mid-1980s. It is a compact, microprocessor-based NC that integrates the operator panel, PLC, NC kernel, and servo interpolation on a backplane populated by a small number of large-format PCBs. A typical machine is built from:

The 6FX1132-8BB01 card carries the NC CPU (80186-class), the PLC interpreter, and the V.24 transceivers. The card exposes two independent V.24 channels to the outside world:

• X121 (COM1 / front) – 25-pin male D-sub on the front bezel. Routed to the front connector via a short ribbon inside the cabinet.
• X131 (COM2 / internal) – 25-pin male D-sub directly on the PCB at the rear of the card, intended for OEM line-side communication but fully usable for commissioning.

Both ports default to 9600 bit/s, 7 data bits, even parity, 2 stop bits (9600/7E2) when the system is fresh, but the baud rate is settable through machine data MD 5010.x. The PLC runtime loads the STEP 5 image from EPROM at power-up; if the image is invalid or absent, the PLC drops into STOP and the control will not enable the axes or spindle.

3. The 6FX1132-8BB01 NC Card

The 6FX1132-8BB01 is the production NC card for the Sinumerik 810T GA1 and GA2 hardware generations. Key specifications:

The card supports a third program-storage medium: the ASM module (a Siemens-specific EPROM carrier) which can be programmed off-line with the STEP 5 source and then plugged into the socket on the card. This is the only fully RS-232-independent loading path the 810T offers, and it is the path that becomes relevant when both V.24 ports are unusable.

4. RS-232 / V.24 Communication Path

The 810T transfers PLC programs and machine data using a Siemens-proprietary protocol layered on V.24. PCIN, supplied with the control, is a DOS / Windows terminal that speaks this protocol. A working data-transfer session requires all of the following to be correct:

1. Correct cable: straight-through for COM1 on most PCs (DTE-to-DCE), or a null-modem cable depending on the PC's serial port gender and the 810T's DTE/DCE wiring.
2. Baud, parity, stop bits match the active MD 5010 set on the control.
3. Handshake mode: Xon/Xoff (DC1/DC3) is default; RTS/CTS is selectable on later 810T firmware.
4. Operator-panel key sequence to put the channel into "data-in" mode (typically SETUP > DATA IN/OUT > PLC on the 810T GA2 panel).

If a session starts and immediately aborts, the cause is almost always one of:

5. Why Keypad PLC Loading Is Not Possible

The 810T operator panel is a serial terminal to the NC CPU; the NC CPU exposes a defined set of editable objects:

• R-parameters (R0 … R99, R100+ as extended) – free-form 32-bit integers and reals.
• Zero offsets (G54–G59), tool offsets, setting data.
• Machine data in the field-service MD view (password-protected).
• PLC status / I/O forcing in monitor mode.

The PLC program – the list of STEP 5 statements that the interpreter executes every PLC cycle – is not an editable object from this menu tree. It is a binary image compiled off-line (or assembled on the optional PG615 programmer) and stored either in the EPROM/ASM module or downloaded as a single block into the card's PLC memory region. The keypad driver in the 810T firmware simply has no command path to write a STEP 5 program, byte by byte, into the PLC code memory.

Historical field anecdote: at least one 810T-equipped lathe (a Solifer-1 conversion) was reported to have been "keyed in by hand," but in practice this was the R-parameter and zero-offset set, not the PLC program. The PLC image was always still pushed through COM1 by the service engineer. Treating the keypad as a PLC loader is therefore a dead end; the engineering effort should instead be focused on restoring one of the three valid loading routes.

6. The Three Supported PLC Loading Methods

For a 810T with a 6FX1132-8BB01 card, the PLC user program can be brought into the card in exactly three ways.

6.1 ASCII text via RS-232

The PLC source is exported as a plain ASCII STEP 5 listing (file extension .S5D or .PLC depending on the toolchain) and downloaded through PCIN using the Data In / PLC menu. The control stores the image in the volatile PLC RAM and the system then burns it into the on-card EPROM via the resident PROM programmer (if fitted). This is the most common method in the field because it requires no additional hardware beyond a PC with a serial port.

6.2 STEP 5 programmer via RS-232

A Siemens PG615 / PG730 (or any modern PC running STEP 5 V7.x with a V.24 cable) connects to either X121 or X131 and uses the PLC > Transfer > Block dialog. This method supports online edit, online documentation, and status, but functionally it is the same byte-stream as method 6.1. The PG route is preferred when the service engineer must debug contacts and set outputs in real time.

6.3 ASM module programmed off-line

If both V.24 channels are electrically dead – an unusual but not unknown condition on a 35-year-old card – the only remaining option is an ASM (AsSiemens Module), an EPROM carrier that is programmed on a standalone EPROM burner and then physically inserted into the socket on the 6FX1132-8BB01. The control reads the ASM at every cold start before normal PLC execution. The machine tool builder, in principle, shipped a programmed ASM with the machine; in practice very few builders ever did, so the field engineer usually has to re-create the ASM from the original STEP 5 listing using a third-party EPROM programmer (e.g., Data I/O, BP Microsystems) and a 27C256 or 27C512 EPROM, depending on the PLC size.

7. PCin Tool and R-Parameter Handling

PCIN is the official Siemens transfer utility for the 810/820 family (PCIN32 for 32-bit Windows is the modern build). It handles three object classes:

The 810T firmware allows the keypad to receive R-parameter updates that the PC pushes down COM1 even after a failed PLC transfer, because R-parameters live in a different address space. This is why the symptom "PCin works for R-parameters but not for PLC" is so common on aging cards: the V.24 transceiver is usually fine, the cable is usually fine, but the PLC block-download path uses a longer timeout and a stricter handshake. The diagnostic tree in the next section walks through this.

8. Try the Second V.24 Interface First

Before declaring the 6FX1132-8BB01 card faulty, always try the second V.24 port (X131). The 810T card has two independent V.24 transceivers; it is common to see one fail (typically from ESD at the front panel) while the other remains fully functional.

1. Power down the control and open the cabinet.
2. Locate the 6FX1132-8BB01 card (the largest card, usually on the far left or far right of the backplane).
3. Identify connector X131: a 25-pin male D-sub directly on the PCB, distinct from the front-panel X121 wiring.
4. Connect a known-good null-modem cable from the PC's COM1 to X131.
5. Power up, put the control in Data In/Out > PLC mode, and run the PCIN download.

Where the card sits in a tight slot, X131 may be inaccessible without removing the card one slot. In that case a short adapter ribbon from X131 to an unused hole in the cabinet bulkhead is the standard field practice. Many retrofit builders wire X131 to an external 9-pin D-sub on the cabinet as part of the original commissioning – check for this first.

9. Diagnostic Decision Matrix

Use the following matrix to localize the fault before attempting any card swap.

10. Card Replacement and Sourcing

If the diagnostic chain points to the 6FX1132-8BB01 card itself being defective, the practical replacement paths are:

1. Pull a known-good card from another machine in the same fleet and re-load the user program, R-parameters, and machine data from backup. This is the cheapest and fastest path for shops with more than one 810T.
2. Source a used card from the surplus market (eBay, industrial surplus dealers). Verify the suffix is exactly 8BB01; the 6FX1132-8BB00 and 6FX1132-8BB02 cards are mechanically compatible but have different machine-data defaults and may not accept a user program compiled for the 8BB01 variant.
3. Repair the card: the most common failures on the 6FX1132-8BB01 are the 1488/1489 V.24 driver pair and the MAX232-class transceiver, the 80186 CPU socket, and the lithium battery. All are standard through-hole parts and a competent electronics workshop can revive most boards.
4. Modernize: replace the entire 810T control with a Sinumerik 840D sl or a generic FANUC-based retrofit. This is the only option for shops that need current spare-part support and modern HMI features.

For the PLC program itself, always archive a copy on a PC-resident hard drive as both the original STEP 5 source (so it is editable) and the binary image (so it can be re-flashed into a replacement card). The 810T has no remote firmware-update mechanism, so the only copy of the user program is the one the field engineer keeps.

11. Step-by-Step Recovery Procedure

The following procedure is the recommended field workflow for a 810T with a 6FX1132-8BB01 card that will not accept PLC data over the front V.24 port.

Prerequisites

• Backup copy of the PLC source (STEP 5 ASCII) on a PC.
• Backup copy of the NC machine data and R-parameters.
• Null-modem RS-232 cable, 25-pin male to 9-pin or 25-pin female (depending on PC), tested with a loopback plug.
• PC with PCIN32 (or PG615/PG730 with STEP 5).
• Access to the rear of the cabinet; ESD wrist strap.

Procedure

1. Verify the cable: with the 810T powered down, disconnect the front V.24 cable and fit a loopback plug to the PC end. Run a PCIN self-test. Replace the cable if characters do not echo.
2. Connect to X121 (front port): power the 810T, enter the Setup menu, navigate to Data In/Out > Interface and confirm the active baud and handshake. Set the PC to the same values in PCIN Setup > Interface.
3. Send a small R-parameter file (e.g., a single R5010 = 1). Confirm ACK on the PC and the new value on the operator panel. If this fails, jump to step 4; if it succeeds, the cable and V.24 driver are good.
4. Send the PLC program: in PCIN, Data In > PLC, select the STEP 5 ASCII file, and start the transfer. Watch the progress bar; the 810T will ACK each block. If the transfer stalls or aborts on the first block, reduce the baud to 4800.
5. Verify PLC state: after transfer, the operator panel should show PLC RUN. If PLC STOP, the image was rejected – re-export the source with the matching CL800 target and retry.
6. If step 4 fails after retry at 2400/7E2: power down, move the cable from X121 to X131, repeat from step 2. X131 is electrically separate from the front-panel transceiver and frequently survives a failure that takes down X121.
7. If both X121 and X131 fail: suspect a hard V.24-driver failure on the card. Repair the 1488/1489 pair (typically ICs on the 6FX1132-8BB01 are socketed), or swap the card.
8. If both ports are dead and no spare card is on hand: burn the PLC source into an ASM EPROM with a stand-alone programmer and plug it into the ASM socket. This is the only way to load the PLC without using RS-232 at all.

Verification

• Operator panel shows PLC RUN and NC READY within 30 seconds of power-up.
• Reference points can be approached in JOG mode.
• A simple M-code (e.g., M03 spindle CW) executes and the spindle relay closes.
• All four tuning R-parameters R5010, R5011, R5013, R5016 read back from the panel exactly as in the backup file.
• An end-to-end program run (a safe G0/G1 block) completes without PLC STOP or alarm 6000-series (PLC-generated alarms).

12. Preventive Recommendations

• Replace the 3.6 V lithium battery on the 6FX1132-8BB01 preventively every 4 years, irrespective of the BATTERY LED state.
• Archive the PLC source as plain ASCII STEP 5 plus a binary .BIN image after every change; store on at least two media.
• Pin a printed copy of the active machine data set inside the cabinet door.
• Mark X121 and X131 on the cabinet wiring diagram so the next service engineer knows which port is which.
• Keep at least one spare 6FX1132-8BB01 card on the shelf for production-critical lathes; used cards are becoming scarce and prices rise yearly.

13. Frequently Asked Questions