# Encoding a tag

The **Encode** tab copies an NFC card's UID onto a UHF tag in four steps.

## 1. Tap the NFC card

The UID and the [NXP originality](nxp-originality.md) status appear in step 1. A short
beep confirms the tap was registered.

## 2. UHF tag check

The app scans for the configured duration (default 3 s) and requires exactly one tag
in range. Zero or multiple tags stop the workflow with an error — isolate a single
tag and press *Scan again*.

## 3. Confirm the write

The screen shows the tag's current EPC (with RSSI) and the new EPC to be written. If
the tag already carries a UID from a *different* card, an overwrite warning is shown.
Press **Write tag**.

## 4. Write, lock, verify

The app writes the EPC, sets the passwords, locks the tag (when locking is enabled),
and verifies the result by reading the tag back. Success is signalled with a green
flash.

~~~gallery w=210 scroll
![1. Waiting for card](assets/encode-wait-for-card.png)

![2. UHF check](assets/encode-uhf-scan.png)

![3. Confirmation](assets/encode-confirm-write.png)

![4. Success](assets/encode-success.png)
Signalled with a green flash and a success tone.

![Already encoded](assets/encode-already-encoded.png)
Shown when the tag already carries this card's UID.

![Invalid signature](assets/encode-invalid-signature.png)
Shown when the card's NXP originality signature does not validate.
~~~

~~~gallery w=210 scroll
![1. Waiting for card (tablet)](assets/encode-wait-for-card_l.png)

![2. UHF check (tablet)](assets/encode-uhf-scan_l.png)

![3. Confirmation (tablet)](assets/encode-confirm-write_l.png)

![4. Success (tablet)](assets/encode-success_l.png)

![Already encoded (tablet)](assets/encode-already-encoded_l.png)

![Invalid signature (tablet)](assets/encode-invalid-signature_l.png)
~~~

## Continuous mode

**Continuous mode** returns to step 1 automatically two seconds after a success —
convenient for encoding a batch of cards.

## Already-encoded tags

If the scanned tag already carries this card's UID, the app reports *"re-writing is
not required"* instead of writing.

> [!NOTE]
> With locking enabled the app silently completes any missing passwords/locks first —
> this also repairs tags left half-secured by an interrupted write. **Write again
> anyway** forces a full re-write.

## If a write fails

> [!TIP]
> If a write fails mid-sequence (e.g. the tag left the field), simply scan again —
> the workflow re-reads the tag's current state and the whole sequence is safe to
> re-run.