# COSMIIC Remote Module Network Interface

The Remote Module Network Interface is the shared circuit block present on every COSMIIC remote module (PG4, BP2, and derivatives). It bridges the AT90CAN128's built-in CAN controller to the implanted 2-conductor network, extracts regulated 5V from the network supply, and fans out to 4 ports (1 upstream in + 3 downstream out) for branching tree topology.

## How it works

Every remote module connects to the COSMIIC implanted network through a single 2-conductor cable. That cable carries both the CANopen differential bus and the DC supply voltage on the same conductors (NET_P = CANH / supply+, NET_N = CANL / supply return). The network interface circuit:

1. **Extracts regulated 5V** — NET_P (4.7–9.6 V from the PM) feeds the U2 LDO; regulated 5V powers the AT90CAN128 and the CAN transceiver
2. **Transceives CAN** — U1 (TJA1050T) bridges the AT90CAN128's digital CANTX/CANRX pins to the physical CANH/CANL bus
3. **Fans out to 4 ports** — J1–J4 connectors branch the same CAN bus to 1 upstream input + 3 downstream outputs
4. **Hardware node addressing** — MC_ANODE exposes the hardware node address line to the AT90CAN128

U1's Rs pin is pulled low through R1 (10 kΩ) for slope-controlled mode, which limits dV/dt on the bus edges and reduces EMI — important for implantable devices.

## Hardware

| Parameter | Value |
|-----------|-------|
| CAN Controller | AT90CAN128 built-in (ISO 11898, CAN 2.0B) |
| CAN Transceiver | NXP TJA1050T (SOIC-8, 1 Mbps, 5V) |
| LDO Regulator | MIC5205-5.0YM5 (SOT-23-5, 5V, 150 mA) |
| Network Cable | 2-conductor (CAN differential + power superimposed) |
| Network Ports | 4 total — J1 upstream in, J2–J4 downstream out |
| Topology | Branching tree (up to 24 nodes from a single PM) |
| Network Voltage | 4.7–9.6 V (adjustable from PM) |
| Output Voltage | 5 V regulated |
| Protocol | CANopen |
| Node Addressing | Hardware-configured (MC_ANODE) |
| PCB Size | 32 × 24 mm Adom molecule |

## Components

| Ref | Part | Value | Package | JLCPCB |
|-----|------|-------|---------|--------|
| U1 | NXP TJA1050T | CAN transceiver, 1 Mbps | SOIC-8 | C6952 |
| U2 | MIC5205-5.0YM5 | 5V LDO, 150 mA, 16V max in | SOT-23-5 | C89758 |
| J1–J4 | 2-pin header | COSMIIC network port | 2.54mm pitch | — |
| C1 | 100nF | TJA1050T VCC decoupling | 0402 | C1525 |
| C2 | 10µF | LDO input cap | 0805 | — |
| C3 | 22µF | LDO output cap (stability) | 0805 | — |
| C4 | 100nF | TJA1050T VREF bypass | 0402 | C1525 |
| R1 | 10 kΩ | TJA1050T slope control (Rs) | 0402 | C25744 |

> **Production note:** For the full 4.7–9.6 V network range, replace U2 with LM1117S-5.0 (C126028, SOT-223-3, 800 mA) which handles up to 15 V input.

## Signal Net Names

| Net | Description |
|-----|-------------|
| `NLTXCAN` / MC_CANTX | CAN TX from AT90CAN128 to U1.TXD |
| `NLRXCAN` / MC_CANRX | CAN RX from U1.RXD to AT90CAN128 |
| `NLTXCANBUS` / CANH | CAN bus positive on network cable |
| `NLTXCANBUS` / CANL | CAN bus negative on network cable |
| `NLANODE` / MC_ANODE | Hardware node address input |

## Machine Contacts

| Contact | Side | Function |
|---------|------|----------|
| MC_CANTX | Left | CAN TX from AT90CAN128 → U1.TXD |
| MC_CANRX | Left | CAN RX from U1.RXD → AT90CAN128 |
| MC_VCC5V | Left | 5V regulated output to module |
| MC_GND   | Left | Ground reference |
| MC_VIN   | Right | Network supply input (4.7–9.6V) |
| MC_CANH  | Right | CAN bus positive |
| MC_CANL  | Right | CAN bus negative |
| MC_ANODE | Right | CANopen node address |

## Architecture

```
        Network Cable (2-wire: NET_P/CANH and NET_N/CANL)
                │
    ┌───────────▼─────────────┐
    │   J1 — Port 1 (in)      │
    └───────────┬─────────────┘
                │
    ┌───────────▼──────────────────────────────────┐
    │        Network Interface (32×24mm)           │
    │                                              │
    │  ┌──────────────┐   ┌────────────────────┐  │
    │  │ U2 MIC5205   │   │ U1 TJA1050T        │  │
    │  │ 5V LDO       │   │ CAN Transceiver    │  │
    │  │ NET_P → 5V   │   │ CANTX/CANRX (MCU)  │  │
    │  └──────┬───────┘   │ CANH/CANL (bus)    │  │
    │         │ VCC       └──────┬──────────────┘  │
    │         └──────────────────┤                 │
    │                            │ CANH / CANL     │
    └────────────────────────────┼─────────────────┘
                │          │          │
    ┌───────────▼─┐ ┌───────▼──┐ ┌───▼────────┐
    │ J2 (out 1)  │ │J3 (out 2)│ │J4 (out 3)  │
    └─────────────┘ └──────────┘ └────────────┘
```

## CANopen Protocol

The PM acts as NMT master; remote modules are NMT slaves.

| Message Type | Direction | Purpose |
|--------------|-----------|---------|
| NMT | PM → Module | State machine transitions (Operational, Pre-op, Reset) |
| SYNC | PM → All | Cyclic timing reference (controls stimulation frequency, data windows) |
| SDO | Bidirectional | Point-to-point Object Dictionary read/write (configuration, testing) |
| PDO | Module → PM | High-speed broadcast of sensor data / stimulation status |
| Emergency | Module → PM | Fault reporting |

## Build

**EDA:** tscircuit (TSX) — source bundle included in Files below.

**LDO note:** Production modules use LM1117S-5.0 (C126028, SOT-223) which handles the full 4.7–9.6V network range. The SOT-23-5 MIC5205 in this reference design targets bench testing where network voltage is kept ≤6V.

**Firmware:** [COSMIIC-Community/Implantables-PG4-App](https://github.com/COSMIIC-Community/Implantables-PG4-App) / [Implantables-BP2-App](https://github.com/COSMIIC-Community/Implantables-BP2-App) — C, AVR toolchain

## Source

All design files are open source under CERN-OHL-P-2.0 (hardware) and MIT (firmware).

## Files

| File | Description |
|------|-------------|
| `cosmiic-network-interface-source.tar.gz` | tscircuit project source (lib/index.tsx, package.json, config) |
| `schematic.svg` | Circuit schematic (all connections) |
| `pcb.svg` | PCB layout (32×24mm, component placement) |
| `3d.glb` | 3D board model |

## Reference Implementation

The equivalent analog circuit appears as a dedicated schematic sheet in every remote module Altium project:

- **PG4** — page 4 of 8 ("CAN Interface") in [COSMIIC-Community/Implantables-PG4-Hardware](https://github.com/COSMIIC-Community/Implantables-PG4-Hardware)
- **BP2** — page 4 of 6 ("Network Interface") in [COSMIIC-Community/Implantables-BP2-Hardware](https://github.com/COSMIIC-Community/Implantables-BP2-Hardware)

## NSF Relevance

The standardized remote module network interface enables multi-node implantable research systems with a single power and communication cable per branch. Researchers can add sensing or stimulation nodes to a running implant without architectural changes, enabling adaptive closed-loop protocols with real-time bidirectional data flow.

## Science Drivers

implantable_healthcare

Created by: noah
Version: v1
Category: other