# Flashing _Writing new firmware_ Flashing writes new firmware onto the box, to update or recover it. The box has two chips; flash each separately. With firmware already running, no physical button is needed: a [`REBOOT`](/native/commands/admin.md#reboot) command restarts a chip into ROM download mode (a built-in loader that takes firmware over serial), then a flashing tool writes the image. ## Two chips _Flash each separately_ Pick the chip with the [`REBOOT`](/native/commands/admin.md#reboot) `target` byte, then flash it over the link in the table. | Chip | Reboot | Flashed over | | --- | --- | --- | | [Device chip](/native/architecture.md) | `target = 0` | The same [CH343](/native/transport.md) serial link, with [`esptool`](https://github.com/espressif/esptool). | | [Host chip](/native/architecture.md) | `target = 1` | Its own USB connection; the device relays the reboot over the inter-chip link. | ## Version scheme _major.minor.patch_ Read the running version with [`QUERY(VERSION)`](/native/commands/requests.md#version). ## Notes > **Warning** > > - The [`REBOOT`](/native/commands/admin.md#reboot) path needs working firmware to receive the frame. A chip with no firmware yet (a first flash) or a bad image can't, so enter download mode the hardware way: hold the chip's BOOT button while you reset or power on the box. > - A run reboot (`target = 2` or `3`) is the only software cold-reboot; `DTR`/`RTS` aren't wired to a reset on this board. > - After a download reboot the serial port sits in the ROM bootloader (plain ASCII the [frame decoder](/native/frame.md) ignores) until you finish flashing or power-cycle. > - Persisted per-box data survives an app reflash. > **Note** > > The `medius` crate's [flash feature](/library/features/flash.md) does this from Rust.