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Verify current device count

Press MOD key, navigate to System > Hardware Configuration. Review the list of detected PLB (PLCBox), MB (ModBox), TE (TouchEncoder), and UxC (Universal Interface) devices. Record the total count and compare to the %1 value in the alarm message.

The alarm message explicitly shows 'Current: %1; perm.: %2' — %1 is detected devices, %2 is your maximum allowed. This immediately tells you how many devices need to be removed or reconfigured.

Review TNC model specifications

Check the technical documentation for your specific TNC model (320, 530, 620, 640, iTNC 530) to confirm the maximum number of PL6000 expansion devices supported. Note that different control variants and MC (Main Computer) versions may have different limits.

TNC 640 typically supports more expansion devices than TNC 320. The CC (Communication Controller) version also affects device limits — check the label on the CC6xxx module.

Identify non-essential devices

Determine which PLB/MB/TE/UxC devices can be removed or consolidated. Prioritize keeping devices essential for machine operation. Document any TouchEncoder (TE) interfaces or PLCBox modules that may be redundant or used for optional features.

Before disconnecting any device, ensure machine operation will not be compromised. Removing active PLB or MB modules during PLC program execution may cause machine malfunctions.

Power down and remove excess devices

Perform a complete power-down of the control and machine. Physically disconnect excess PL6000 devices from the system bus. Ensure proper bus termination is maintained. Power up and verify the alarm is cleared and device count is within permitted range.

Always maintain proper PL6000 bus termination. The last device on the bus must have termination enabled or a termination resistor installed.

Check device addressing

Access MOD > System > Hardware Configuration and review the address assignment of all PLB, MB, TE, and UxC devices. Verify that each device has a unique address on the PL6000 bus and no conflicts exist.

PL6000 devices typically use rotary switches or DIP switches for address selection. Physical address settings must match what the control detects.

Inspect physical address switches

Power down the system. Physically inspect each PLB, MB, TE, and UxC module's address switch settings. Document each address and verify no duplicates exist. Check that addresses are sequential and within the valid range for each device type.

Address switches should only be changed when power is OFF. Changing addresses under power can cause bus communication errors.

Reset PL6000 bus configuration

In MOD functions, access the system configuration and perform a hardware scan/reset of the PL6000 bus. This forces the control to re-enumerate all connected devices and rebuild the device table. Power cycle after the reset.

After bus reset, the control will rebuild the device list. If the count is still incorrect, a hardware fault is likely present rather than a configuration issue.

Verify bus cable integrity

Inspect all PL6000 bus cables for damage, proper seating, and correct pinout. Poor connections or damaged cables can cause signal reflections that make the control detect ghost devices.

Use only Heidenhain-specified PL6000 cables with proper shielding. Generic cables may cause communication errors and false device detection.

Identify recently added or suspect devices

Review maintenance logs and determine if the alarm appeared after adding or replacing a specific PLB, MB, TE, or UxC device. Also check MOD > System > Hardware Configuration for any devices showing unusual status or communication errors.

Devices with intermittent communication often show repeated appearance/disappearance in the hardware list or status indicators that flash between OK and error states.