# UART Communication Plan

## Overview

The first hardware version will use plain UART over CAT5 between the Pico dashboard and the ESP32 cargo controller.

UART is simpler than RS-485 and should be reliable enough for the short cable run inside the Xterra.

RS-485 remains a fallback if UART proves unreliable.

## Architecture

Pico Dashboard
↓
UART over CAT5
↓
ESP32 Controller

Backup:
WiFi HTTP API

Fallback:
RS-485 over CAT5

## UART Wiring

Pico TX -> ESP32 RX
Pico RX <- ESP32 TX
Ground  <-> Ground

## Planned Baud Rate

Initial:
115200 baud

Future testing:
- 57600 baud if noise becomes an issue
- 230400 baud if higher update rates are needed

## Message Format

Messages will use newline-delimited JSON.

Example request:

{"type":"status_request"}

Example response:

{"type":"status_response","data":{"battery":{"soc":82}}}

Each message ends with a newline character.

## Failure Handling

If no valid response is received within the timeout:

- Dashboard shows communication warning
- Last known values remain visible
- Relay commands fail safely
- WiFi backup may be attempted if enabled

## Why UART First

Advantages:

- Fewer parts
- Easier wiring
- Easier debugging
- No direction-control pin
- No transceiver modules required
- Works well over short distances

## Why RS-485 Is Still Available

RS-485 may be used later if UART has issues caused by:

- Alternator noise
- Relay switching noise
- Fridge compressor noise
- Inverter noise
- Long cable run
- Ground noise

The software should keep a transport abstraction so UART and RS-485 can be swapped without changing the application protocol.