Panasonic GT HMI — No Communication with FP PLC

Panasonic · intermediate · 20 min

A Panasonic GT programmable display that won't talk to an FP PLC shows its error in the top-right corner of the screen. Learn the ER0021/ER0022 comm codes, why the PLC must be set to Computer Link, and the GTWIN/FPWIN pass-through gotcha.

ℹ️ On a Panasonic GT display, error codes appear in the upper-right corner of the screen. For FP-PLC comms, ER0021 is a data error and ER0022 an overrun error — and the PLC port must be set to Computer Link or it won't answer at all.

Where the GT shows the error

On a Panasonic GT-series programmable display (GT01, GT703/704/707…), when a communication problem occurs an error code is displayed in the upper-right corner of the screen. That's the first place to look — it tells you whether the panel is seeing a data/overrun error or simply nothing.

The FP-PLC communication codes

Talking to Panasonic FP-series PLCs, the common comm error codes are:

• ER0021 — a data error during communication.
• ER0022 — an overrun error.

Both point at the serial link quality/settings rather than the application — a mismatch in parameters, noise, or a marginal cable will produce these.

The PLC must be in 'Computer Link'

A classic "it will never communicate" cause: the PLC-side port setting must be set to match 'Computer Link' for the FP device and the GT to talk. If the FP port is configured for a different mode (e.g. programming/MEWTOCOL general-purpose vs. Computer Link as the GT expects), the panel gets no valid response. Set the FP port mode correctly first.

The GTWIN / FPWIN pass-through gotcha

If you're using the pass-through function (programming the PLC through the HMI), note: there are combinations that cannot support simultaneous communication of GTWIN and FPWIN. If either FPWIN or GTWIN is communicating, the other communication stops. So a "comms dropped" while you had both tools open may simply be the two contending — close one.

Check the basics

• Serial parameters in GTWIN's configuration must match the PLC (the GT supports RS232C / RS422(RS485)) — baud, data/parity/stop, station.
• USB (PC↔GT): if transfer fails over USB, remove and reinsert the USB cable and retry sending/receiving.

Step-by-step

1. Read the code in the top-right of the GT screen (e.g. ER0021 data error, ER0022 overrun).
2. Set the FP PLC port to Computer Link to match what the GT expects.
3. Match serial params (RS232C/RS422) in GTWIN to the PLC.
4. Using pass-through? Don't run GTWIN and FPWIN comms at once — one stops the other.
5. USB transfer failing? Reseat the USB cable and retry.

Never do this

Don't assume a recurring ER0022 overrun is just "the HMI" — an overrun usually means the link is marginal (baud too high for the cable run, noise, or a bad converter). Fix the physical link and settings rather than lowering expectations.