---
url: /en/docs/xt-c-485-hia-v3_5/pinout/index.md
---
# Pinout

> The silkscreen reads **top to bottom, viewed from above**.

## Logic Side (2.54 mm)

![Logic-side silkscreen (top to bottom: VIN → RX → TX → GND)](/images/products/xt-c-485-hia-v3_5/XT-C-485-HIA-V3_5-logic-side-silk.webp)

| Name | Flow | Description |
|------|:---:|------|
| `VIN` | — | Supply 3.0 – 5.5 V (3.3 V / 5 V typical) |
| `RX` | Module → MCU | Bus data received by the module goes to the MCU; connect to the MCU's `RX` |
| `TX` | MCU → Module | Data the MCU wants to send goes into the module; connect to the MCU's `TX` |
| `GND` | — | Logic-side ground, common with the MCU |

**Straight-through to the MCU — no crossover**: `TX` to the MCU's `TX`, `RX` to the MCU's `RX`. `TX` is shaped by a Schmitt trigger and drives the transceiver's `RE` / `DE` directly; half-duplex direction switching is automatic, so **the software never handles direction**.

## Bus Side (5.08 mm)

![Bus-side silkscreen (top to bottom: B → PE → A)](/images/products/xt-c-485-hia-v3_5/XT-C-485-HIA-V3_5-bus-side-silk.webp)

| Name | Flow | Description |
|------|:---:|------|
| `B` | Bidirectional | RS-485 B (inverting) |
| `PE` | — | Protective earth — **must be terminated to earth nearby** (the discharge path of the gas discharge tube) |
| `A` | Bidirectional | RS-485 A (non-inverting) |

## Wiring Notes

* **`PE` must be terminated to earth nearby**: the gas discharge tube uses `PE` as its discharge path; with `PE` floating, surge protection is noticeably weaker.
* **Never short the isolated-side `PE` to the logic-side `GND`**: once they share ground, the isolation is gone.
* **Termination**: close the on-board jumper for 120 Ω **only at the two physical ends** of the bus; leave intermediate nodes open.
* **Biasing**: the module provides A pull-up / B pull-down bias; when you build a multi-node network, work out the parallel bias of the whole bus.

## Dimensions

Outline 90 × 20 mm, board thickness 1.6 mm.

![XT-C-485-HIA-V3/5 top view outline and hole positions](/images/products/xt-c-485-hia-v3_5/XT-C-485-HIA-V3_5-top-size.svg)

## Recommended Pad Dimensions

![XT-C-485-HIA-V3/5 recommended pad (footprint) dimensions](/images/products/xt-c-485-hia-v3_5/XT-C-485-HIA-V3_5-package.svg)

Recommended pads: logic side **3.6 × 1.9 mm** (pitch 2.54 mm), bus side **4.4 × 2.2 mm** (pitch 5.08 mm); the remaining locating dimensions are in the drawing above.

> Electrical parameters are in [Specifications](./specs.md); the full parameter table is on the [product page](/en/products/xt-c-485-hia-v3_5/).