PS0001

Press SYSTEM key, navigate to PARAM screen. Check parameter 0020 (I/O channel settings), verify bit 0-2 for parity selection: 00=EVEN, 01=ODD, 10=NONE.

Verify parameter 0021 (stop bit and data bit length). Bit 0 sets stop bits (0=1bit, 1=2bit), bit 1 sets data length (0=7bit, 1=8bit). Confirm these match external device settings exactly.

Check parameter 0022 (baud rate setting). Common values: 0=110, 4=1200, 5=2400, 6=4800, 7=9600, 8=19200. Mismatch causes parity errors even with correct parity setting.

After parameter verification/correction, reset alarm with RESET key. Attempt data transmission test. If alarm persists, proceed to hardware checks.

Parameter write enable switch must be ON to modify I/O parameters. Switch OFF after changes to prevent accidental modifications.

Inspect RS-232C cable (typically 25-pin D-sub at CNC) for physical damage, pinched sections, or proximity to power cables. Maintain minimum 300mm separation from motor cables and inverters.

Never route RS-232C cables through the same cable duct as servo motor or spindle motor cables.

Verify cable uses proper shielded twisted-pair construction. Check shield continuity with multimeter and confirm 360-degree shield grounding at CNC end only (not both ends to avoid ground loops).

Replace RS-232C cable with known-good shielded cable maximum 15 meters length. Use ferrite cores on both ends if operating near high-frequency noise sources.

Check diagnostic screen SYSTEM > DIAGNOSIS > SERIAL for communication error counters. Note error frequency pattern. Intermittent errors indicate noise; consistent errors indicate parameter or hardware fault.

Perform loopback test: Connect pins 2 and 3 (TXD to RXD) at CNC RS-232C connector. Navigate to EDIT mode, attempt to output a simple program. If alarm occurs during loopback, confirms CNC hardware fault.

Ensure no external devices are connected during loopback test to isolate CNC hardware.

Check SYSTEM > DIAGNOSIS > I/O for board detection status. Verify I/O Link-i or I/O Link II board is recognized. Missing board indication requires reseating or replacement.

If multiple I/O channels available, test alternate channel (JD1A vs JD1B connector). Modify parameter 0020 bit 4-6 to select different channel. Successful communication on alternate channel confirms primary channel failure.

Replace RS-232C board or main CPU board if loopback test fails. Contact Fanuc service for board-level diagnostics. Check for available software updates (Series 0i: check ladder, Series 30i/31i/32i: check system software version).

Board replacement requires system parameter backup and proper ESD precautions. Power OFF and wait 5 minutes before removing boards.