Sinumerik 802C Base Line: M01, MD Backup, and PLC Programming

1. System Overview

The SINUMERIK 802C base line is a microprocessor-based numerical control system designed for cost-sensitive machine tools that retain analog servo and spindle drives. The platform targets simple turning, milling, and drilling cells where digital-drive buses would inflate cabinet cost. The control integrates the HMI, the NC kernel, and a PLC on a single front-panel-mountable unit, eliminating the separate PLC rack found on higher-tier SINUMERIK lines.

Key field characteristics that distinguish a base line installation:

• Analog ±10 V command interface for axis and spindle drives (set-point value outputs through onboard DACs).
• Digital I/O only, no PROFIBUS-DP drive bus.
• Integrated PLC that executes ladder logic on every NC cycle (typical OB1 tick).
• Compact operator-panel form factor suitable for mid-sized lathes and knee-mill retrofits.
• Bero (proximity-switch) referencing instead of absolute encoders on cost-down axis configurations.

For the canonical commissioning manual that documents hardware layout, connector pinning, and first-power-up behavior, refer to the official SINUMERIK 802C base line commissioning manual (PDF) hosted on the Siemens Industry Online Support portal. All operator-panel, MD, and PLC procedures in this article are consistent with the 0803 edition of that document.

2. Hardware Architecture and Cabling

The 802C base line chassis contains the following logical blocks: the operator panel (HMI) with monochrome or color LCD, the NC-CPU module, the analog set-point card for axes and spindle, the digital I/O card (24 V DC), the integrated PLC processor, and the operator-panel keyboard that doubles as the M-function and feed-hold trigger surface.

When the cabinet is wired with the X axis using only a Bero cam reference and the spindle running without an encoder, the control must be configured accordingly: spindle indexing, thread-cutting synchronization, and rigid-tapping will not be available, and the relevant MD bits must be cleared to suppress the resulting alarms. This is a common cost-optimization on retrofit 802C installations.

3. M01 Optional Stop — Behavior and Control

The M01 command is a programmable optional stop. When the part program executes a block containing M01, the control reads the operator-panel selector (commonly labeled OP or M01 on the dedicated key) and either halts at the M01 block for operator intervention or continues processing as if M01 were a no-op.

3.1 Mechanical selector on the operator panel

Most CNC machine builders wire a physical two-position selector or a momentary key on the operator panel that drives a discrete 24 V input into the digital-I/O card. The PLC program reads that input and writes the corresponding interface flag (commonly V39000001.0 on the 802C base line for the OP-key equivalent, or DB20.DBX0.0 depending on builder wiring). The NC interprets the flag and decides whether to stop at M01.

3.2 Program-merker override

If no panel selector exists, the builder can install a permanently-low or permanently-high logic in the PLC program so M01 always behaves one way. Service engineers use this to verify, during commissioning, that the OP-flag wiring is correctly mapped: with the panel selector in either position and the M01 block reached, the operator can observe whether the axis freezes at the block or passes through.

3.3 Procedure to enable M01 stoppage

1. Place the operator-panel selector in the ON (or STOP) position before cycle-start.
2. Confirm in the program that M01 is entered in a block on its own (or with a comment). The block N50 M01 ; check workpiece diameter is the canonical pattern.
3. Start the part program. At the M01 block the spindle typically continues rotating, but feed-hold is asserted, the axes decelerate, and STOP appears in the channel-status line.
4. Press CYCLE START to resume from the M01 block.
5. Press RESET to abort if a tool change or inspection is required.

3.4 Interaction with /-skip and motion-stop overlap

The 802C base line treats M01 like M00 with respect to spindle and coolant: M01 typically does NOT stop the spindle by default. If spindle-stop on M01 is required, the part program must include a separate M05 block immediately before M01, or the PLC must be programmed to assert spindle-stop when the OP-stop flag is read at the M01 block boundary. Builders on a 802C retrofit often add this to their standardized part-program header.

4. Machine Data (MD) — Structure, Backup, and Restore

Machine Data is the persistent parameter set that calibrates axes, sets velocity limits, configures encoder direction, configures spindle ratios, and defines the M/H/T auxiliary mappings. The MD is the highest-leverage target for a maintenance engineer because a corrupted or mis-configured MD is the typical root cause of an 802C base line refusing to traverse, refusing to home, or raising cascading axis alarms on first power-up.

4.1 MD logical organization

The 802C base line MD is grouped into axis-specific and general sections. Each MD entry has a numeric identifier (for example MD20050 for axis-referencing configuration, MD20150 for axis encoder coarse resolution, MD31020 for spindle encoder resolution, MD32000 for max spindle speed). Service engineers typically print the MD dump using the RS232 serial interface and a PC configured with the Siemens archiving tool.

4.2 Backup workflow via RS-232

1. Connect a PC running a terminal emulator (or the Siemens archive tool) to the 802C base line RS-232 service port at the cabinet.
2. Set the terminal to 9600 / 8-N-1 (the documented default on this platform unless the cabinet-architect MD overrides it).
3. From the operator panel navigate to Commissioning → Series start-up → Machine data → Read out.
4. Save the binary or text dump to a uniquely named file. Use the machine serial number, last commissioning date, and software version stamp as the filename suffix.
5. Validate the file size and checksum against the panel prompt before storing it offsite.

4.3 Restore workflow

1. Connect the same PC, restore the file with the matching baud rate and parity.
2. From the operator panel navigate to Commissioning → Series start-up → Machine data → Read in.
3. Wait for the control to display MD load complete. Do not power-cycle during this interval.
4. Power-cycle the control and verify that the home position, soft limits, and feed-rate overrides match the pre-backup state.

4.4 Manual MD file editing on PC

The dump is plain ASCII (or a simple framed binary) so a text editor can be used to modify a single MD line before read-in. Common edits include:

• Adjusting MD20150 for a swapped encoder pulse count.
• Setting a nonzero value in MD32000 after a spindle motor swap.
• Enabling MD30200 for an encoder index pulse when an encoder is retrofitted.

5. Program Management — Memory, Selection, and Execution

The 802C base line stores part programs in a battery-backed SRAM or a compact flash module depending on the build year. Operators select programs through the panel, and the file is then loaded into the NCK interpreter for execution.

5.1 Program navigation path

1. Press the Program hard-key on the operator panel.
2. Open the Program list soft-key to view all files stored under the active program directory (/_N_MPF_DIR for main programs, /_N_SPF_DIR for subprograms, /_N_CST_DIR for cycles).
3. Use the cursor keys to position over the required program; press the Select soft-key to mark it as the active part program.
4. Press CYCLE START to execute.

5.2 Memory types and limits

5.3 Program transfer from PC

The 802C base line accepts programs sent via RS-232 from a PC running PCIN or a compatible terminal tool. The handshake uses XON/XOFF by default. A typical part program header for an 802C base line turning cell is shown below.

;PART_001.MPF
N10 G54 G90 G97 S1500 M03
N20 T1 D1
N30 G00 X50.0 Z2.0
N40 G01 Z-30.0 F0.2
N50 M01 ; inspection
N60 G00 X100.0 Z100.0
N70 M05
N80 M30

5.4 Common program-selection faults

• "Program not found": file is on a non-default directory; verify MD11200 default-path setting.
• "NCK identifier invalid": file-name character set violation (802C base line refuses spaces, underscores in unexpected places, or non-ASCII characters).
• No display response: SRAM battery voltage collapsed; replace battery before further edits.

6. Integrated PLC — Loading and Programming

The 802C base line integrates a Siemens-compatible PLC that can be loaded with custom ladder logic for machine-specific I/O mapping, M-function decoding, and safety logic. The PLC program is shipped from the machine builder and is normally loaded once at commissioning.

6.1 PLC loading path

1. Connect the PC running the Siemens PLC programming tool to the 802C base line RS-232 service port.
2. Navigate on the operator panel to Commissioning → PLC → Read in (or Write to PLC depending on direction).
3. Initiate the download from the PC. The PLC enters STOP during transfer and returns to RUN when the block transfer completes successfully.
4. Verify the green PLC-RUN indicator on the panel and observe the first OB1 scan for any first-cycle faults.

6.2 PLC program structure

The base line PLC program typically contains:

• OB1: cyclic scan, reads inputs from the digital-I/O card and writes outputs back each tick.
• FC/FB blocks: M-function decoders (M00–M99 translated into discrete outputs), tool-change sequencer, lube pump timer, spindle-gear-shift sequencer.
• DB blocks: parameter storage for timers, counters, and recipe data that survive a cold restart.

6.3 Example: M01 stop flag handling

The OP-selector that controls M01 stoppage is often wired as I 32.0 and written to the interface flag that the NC reads:

// OB1 cyclic scan
// Read operator-panel M01 selector
      A    I 32.0       // OP-key ON/OFF
      =    M 200.0      // M01 stop request flag
      // Map to NC interface
      A    M 200.0
      =    DB20.DBX0.0  // V39000001.0 equivalent
      // Optional spindle-stop on M01
      A    DB21.DBX40.0 // M-function trigger
      A    DB21.DBX10.0 // M01 active
      =    Q 16.3       // spindle stop output

6.4 PLC backup and restore

The PLC program is stored in flash. To back up, navigate to Commissioning → PLC → Read out and save the binary to a PC file. Restoring follows the read-in path above. Always back up the PLC before any MD change, because some builders key their PLC program to expect specific MD values.

7. Startup Procedure for a New 802C Base Line Installation

1. Visual check: confirm all connectors are seated, terminal screws torqued, and the battery-backed SRAM battery is fresh.
2. Power on: bring up the cabinet in the order documented in the commissioning manual — main breaker first, then control 24 V, then drive DC-bus pre-charge.
3. First-pass axis test: verify Y and Z traverse in both directions using the handwheel or jog keys before addressing X, because Y/Z are typically the simplest configured axes on a base line retrofit.
4. Spindle without encoder: confirm the spindle analog voltage tracks the programmed S-word without an alarm. If ALM 25080 (position-control error) appears, the spindle encoder MD is mis-configured to expect an encoder that is not present.
5. X-axis Bero reference: jog X toward the Bero cam and confirm the NC marks the home position once per cam-pass instead of the typical multi-reed approach.
6. M01 test: load the canonical part program above with the OP selector in ON. Observe that the axes stop at N50.
7. MD dump: back up the MD now (this MD dump represents the commissioned-good state).
8. PLC dump: back up the PLC program the same way.

8. Diagnostics and Fault Code Index

The 802C base line raises NCK and PLC alarms with numeric identifiers displayed in the alarm line. The following table lists the most frequent alarms encountered during commissioning and routine use.

9. Maintenance Schedule

10. Specifications

11. Edge Cases and Field-Proven Caveats

• M01 and modal S-word conflicts: on some retrofits, the PLC sequencer that drives spindle-gear-shift is keyed on the S-word change boundary and will not trigger if M01 fires inside a constant-S block. Verify with a single-block-step test.
• MD file edited on PC and then re-read: the base line strips comments on read-in. Re-numbered MD lines that you hand-edit must still match the canonical axis MD identifier. A misaligned column is the most common silent read-in failure.
• Spindle without encoder and rigid tap: the control will refuse to enter G84 mode entirely. Remove the rigid-tapping cycle from any CNC program that targets a no-encoder spindle or the cycle-start will alarm.
• Bero reference on X-axis and warm-restart: the X home position must be re-acquired by handwheel after every cold start. The base line does not retain the X Bero flag across power-off unless a dedicated SRAM persistence bit is set.
• PLC RUN/STOP toggle: toggling PLC to STOP during a running part program will halt all axes and raise the alarm list above. Always pause and reset before stopping the PLC.