# MR-VMU-Tropic hardware reference

Connectors, pinouts and on-board devices of the NXP MR-VMU-Tropic, an open-source Vehicle
Management Unit (flight controller) built around the
[NXP i.MX RT1064 MCU](https://www.nxp.com/products/i.MX-RT1064). The board carries the Dronecode
DS-009 connector set (telemetry, GPS, I2C, CAN and debug), two ESC headers, a GPS and safety-switch
port, an SPI port for an on-screen display, 100BASE-T1 Ethernet, a microSD slot and a USB device
port. All pin data below comes from the rev F schematic SPF-94468_F. The photos show a rev C board;
the connector positions are the same.

Each card shows three things per pin: the function, the net name in the schematic and the
i.MX RT1064 pad the signal ends up on. Parts in between, such as the CAN transceiver and the
Ethernet PHY, are shown too. Pin 1 is the square pad.

## Board overview

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/overview-top-dark.svg">
  <img alt="MR-VMU-Tropic top view with connector labels" src="resources/img/overview-top.svg" width="880" height="737">
</picture>
</figure>

Not visible here:

- [J1 USB](#main-other-connectors) (bottom view)
- [J12 PWM_B](#main-j12-pwm_b) (bottom view)
- [J13 PWM_A](#main-j13-pwm_a) (bottom view)
- [CN1 MICROSD](#main-other-connectors) (bottom view)

Bottom side, with the two ESC headers, the USB-C port and the microSD slot:

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/overview-bottom-dark.svg">
  <img alt="MR-VMU-Tropic bottom view with connector labels" src="resources/img/overview-bottom.svg" width="880" height="891">
</picture>
</figure>

## Connector index

| Ref | Function | Connector | Details |
|---|---|---|---|
| [Main CN1](#main-other-connectors) MICROSD | microSD card slot | microSD push-push, 8 pins plus card detect | Four-bit SD interface on the first SD host of the chip, used for logging. The card detect switch goes to a separate chip pin. |
| [Main J1](#main-other-connectors) USB | USB 2.0 Type-C device port | USB Type-C receptacle (USB4110-GF-A) | Serial download port of the i.MX RT1064 boot ROM, and the port used for flashing. The board is always a USB device. VBUS can also power the board through protection switch U13. |
| [Main P1](#main-p1-eth) ETH | 100BASE-T1 single pair Ethernet | JST-GH 1x2, top entry | |
| [Main J2](#main-j2-power) POWER | Power module input, 5 V plus battery monitor I2C | Molex Clik-Mate 1x6 (5024430670) | |
| [Main J3](#main-j3-debug) DEBUG | SWD debug and console, DS-009 debug full layout | JST-SH 1x10 | |
| [Main J4](#main-j4-gps) GPS | GPS module with compass, safety switch and buzzer | JST-GH 1x10 (BM10B-GHS-TBT), top entry | |
| [Main J5](#main-j5-can) CAN | CAN FD (TJA1462) | JST-GH 1x4, top entry | |
| [Main J6](#main-j6-spi-osd) SPI (OSD) | External SPI port, meant for an on-screen display board | JST-GH 1x8 (BM08B-GHS-TBT), top entry | |
| [Main J7](#main-j7-aux) AUX | Spare serial port with handshake lines | JST-GH 1x6 (BM06B-GHS-TBT), top entry | |
| [Main J8](#main-j8-telem1) TELEM1 | Telemetry serial port 1 with flow control | JST-GH 1x6 (BM06B-GHS-TBT), top entry | |
| [Main J9](#main-j9-telem2) TELEM2 | Telemetry serial port 2 with flow control | JST-GH 1x6, top entry | |
| [Main J10](#main-j10-i2c) I2C | External I2C bus | JST-GH 1x4, top entry | |
| [Main J11](#main-j11-rc) RC | Serial radio control receiver port | JST-GH 1x4, top entry | |
| [Main J12](#main-j12-pwm_b) PWM_B | Motor outputs 5 to 8 (ESC header) | JST-SH 1x8 | |
| [Main J13](#main-j13-pwm_a) PWM_A | Motor outputs 1 to 4 (ESC header) | JST-SH 1x8 | |

## Power and debug

### Main J2 POWER

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J2-dark.svg">
  <img alt="Main J2 POWER pinout" src="resources/img/main-J2.svg" width="529" height="282">
</picture>
</figure>

This is the main supply of the board. The power module feeds 5 V into pins 1 and 2, and the board
makes its own 3.3 V and 1.8 V from it. Pins 3 and 4 are an I2C bus that reads voltage and current
from the power module.

> Warning: Feed only 5 V into pins 1 and 2. A higher voltage damages the board, because there is
> no regulator behind this connector.

### Main J3 DEBUG

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J3-dark.svg">
  <img alt="Main J3 DEBUG pinout" src="resources/img/main-J3.svg" width="853" height="416">
</picture>
</figure>

Pin 1 is a 3.3 V reference output for the debug probe. Pins 2 and 3 are the serial console. Pins 4,
5 and 6 are the SWD lines of the i.MX RT1064. Pin 9 is the reset line of the chip, which is also
pulled up on the board.

> Warning: Pin 1 is an output at 3.3 V, not a supply input. Use a debug probe that works at 3.3 V
> and never drive this pin.

## Serial ports

### Main J8 TELEM1

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J8-dark.svg">
  <img alt="Main J8 TELEM1 pinout" src="resources/img/main-J8.svg" width="603" height="304">
</picture>
</figure>

Standard DS-009 telemetry layout: 5 V, TX, RX, CTS, RTS, ground. Pin 1 gives 5 V out through ferrite
FL3.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

### Main J9 TELEM2

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J9-dark.svg">
  <img alt="Main J9 TELEM2 pinout" src="resources/img/main-J9.svg" width="596" height="304">
</picture>
</figure>

Same layout and same circuit as TELEM1, on a second serial port of the chip. Pin 1 gives 5 V out.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

### Main J7 AUX

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J7-dark.svg">
  <img alt="Main J7 AUX pinout" src="resources/img/main-J7.svg" width="822" height="304">
</picture>
</figure>

Pin 1 provides a 5 V output. Pins 2 and 3 are assigned to LPUART4, which is used as the AUX serial
port (/dev/ttyS3 in PX4). Pins 4 and 5 are labeled CTS and RTS in the schematic; however, these pins
cannot be multiplexed to the LPUART4 hardware CTS and RTS functions and therefore cannot provide
hardware flow control. If RTS/CTS flow control is required, it must be implemented in software using
these pins as GPIOs.

The signal pins on this connector support several alternative functions through pin multiplexing.
Pins 2 and 3 can be configured as PWM outputs using FlexPWM1 module 3, channels A and B. All four
signal pins can support quadrature encoder or trigger functions through XBAR1, while pins 4 and 5
can instead provide a second CAN interface using FlexCAN2 with an external CAN transceiver.

Use of these alternative functions requires appropriate software and pin-multiplexing configuration
and is left to the user.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

> Note: Confirm that the ESCs do in fact follow the BetaFlight connector standard, as there are
> many ESCs with variations on this pinout. Also note that wires are regularly soldered to pads on
> the ESC side.

### Main J11 RC

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J11-dark.svg">
  <img alt="Main J11 RC pinout" src="resources/img/main-J11.svg" width="550" height="248">
</picture>
</figure>

Serial port for a digital receiver such as ELRS or CRSF. Pin 1 gives 5 V out through a resettable
fuse, so a shorted receiver cannot pull down the board supply.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

## GPS, I2C and CAN

### Main J4 GPS

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J4-dark.svg">
  <img alt="Main J4 GPS pinout" src="resources/img/main-J4.svg" width="762" height="416">
</picture>
</figure>

Pin 1 gives 5 V to the GPS module and pin 8 gives 3.3 V. Both are outputs. Pins 2 to 5 are the GPS
serial port and the shared I2C bus, the same bus as on the I2C connector J10. Pin 6 reads the safety
switch and pin 7 drives its LED. Pin 9 is the buzzer, switched to ground by FET Q1, so the board only
pulls this pin low.

> Warning: Pins 1 and 8 are power outputs. Never feed power into them.

### Main J10 I2C

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J10-dark.svg">
  <img alt="Main J10 I2C pinout" src="resources/img/main-J10.svg" width="557" height="226">
</picture>
</figure>

The same bus as pins 4 and 5 of the GPS connector, so devices here share those addresses. Pin 1
gives 5 V out.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

### Main J5 CAN

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J5-dark.svg">
  <img alt="Main J5 CAN pinout" src="resources/img/main-J5.svg" width="614" height="248">
</picture>
</figure>

The TJA1462 transceiver runs from 5 V and talks to the chip at 3.3 V. CANH and CANL together form the
differential bus, TXD and RXD are the logic lines to the i.MX RT1064. The 120 Ω termination is
fitted, so this port is one end of the bus.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

## Motors

### Main J13 PWM_A

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J13-dark.svg">
  <img alt="Main J13 PWM_A pinout" src="resources/img/main-J13.svg" width="778" height="355">
</picture>
</figure>

Four motor signals for a four-in-one ESC. The pin order follows the
[Betaflight ESC connector standard](https://betaflight.com/docs/development/manufacturer/connector-standard#standard-esc-pin-configuration),
so a standard 8-pin ESC cable fits. The signals carry normal PWM or DShot. The same pads are also
FlexIO1 pins, so DShot or other protocols can be bit-banged by FlexIO. Pin 4 is the ESC telemetry
line, shared with the other ESC header. The ESCs send their UART telemetry (voltage, current, RPM,
temperature) on this one wire, and the chip receives it on LPUART7 in single-wire mode. It is receive
only; the chip never transmits here. Pins 1 (battery voltage) and 3 (current) of the Betaflight
standard are not connected on rev F, so the board does not read battery voltage or current from the
ESC.

> Note: This header has no 5 V pin. Many ESCs have a BEC that powers the flight controller, but
> this board does not use it. It gets its 5 V from the power module on J2 POWER.

### Main J12 PWM_B

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J12-dark.svg">
  <img alt="Main J12 PWM_B pinout" src="resources/img/main-J12.svg" width="778" height="355">
</picture>
</figure>

Same circuit and same Betaflight pin order as PWM_A, for motors 5 to 8. The signals carry normal PWM
or DShot. The same pads are also FlexIO1 pins, so DShot or other protocols can be bit-banged by
FlexIO. Pin 4 is the same shared ESC telemetry line: LPUART7 in single-wire mode, receive only. Pins
1 (battery voltage) and 3 (current) of the Betaflight standard are not connected on rev F, so the
board does not read battery voltage or current from the ESC.

> Note: This header has no 5 V pin. Many ESCs have a BEC that powers the flight controller, but
> this board does not use it. It gets its 5 V from the power module on J2 POWER.

## SPI and Ethernet

### Main J6 SPI (OSD)

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-J6-dark.svg">
  <img alt="Main J6 SPI (OSD) pinout" src="resources/img/main-J6.svg" width="611" height="338">
</picture>
</figure>

Pin 1 gives 5 V to the add-on board, the signal lines work at 3.3 V. Pin 6 is a data-ready input and
pin 7 a reset output. This port is separate from the SPI bus of the on-board sensors.

> Warning: Pin 1 is a 5 V output. Never feed power into it.

### Main P1 ETH

<figure class="pinout-figure" data-pinout>
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="resources/img/main-P1-dark.svg">
  <img alt="Main P1 ETH pinout" src="resources/img/main-P1.svg" width="376" height="204">
</picture>
</figure>

Two wires carry send and receive at 100 Mbit/s. The TJA1103 does the physical layer and talks to the
chip over RMII, so there is no direct link between these pins and a chip pad. Use a twisted pair and
keep both wires the same length. The other end needs a 100BASE-T1 device or a media converter.

### Main other connectors

| Ref | Function | Connector | Notes |
|---|---|---|---|
| J1 USB | USB 2.0 Type-C device port | USB Type-C receptacle (USB4110-GF-A) | Serial download port of the i.MX RT1064 boot ROM, and the port used for flashing. The board is always a USB device. VBUS can also power the board through protection switch U13. |
| CN1 MICROSD | microSD card slot | microSD push-push, 8 pins plus card detect | Four-bit SD interface on the first SD host of the chip, used for logging. The card detect switch goes to a separate chip pin. |

## Buttons and switches

| Ref | Board | Function | Type | Notes |
|---|---|---|---|---|
| SW2 BOOT | Main | Boot mode button | Push button (NANOT 240 AS) | Holding this button while the board powers up pulls boot mode 0 high and starts the serial downloader over the USB port. The second boot mode pin is tied low on the board. |

## Notes

- The connectors marked DS-009 on their card (TELEM1, TELEM2, GPS, I2C, CAN and the debug port)
  follow the Dronecode
  [DS-009 connector standard](https://github.com/pixhawk/Pixhawk-Standards/blob/master/DS-009%20Pixhawk%20Connector%20Standard.pdf),
  so standard cables fit.
- The two ESC headers (PWM_A and PWM_B) follow the
  [Betaflight ESC connector standard](https://betaflight.com/docs/development/manufacturer/connector-standard#standard-esc-pin-configuration),
  so a four-in-one ESC with a standard 8-pin cable fits. Pins 1 (battery voltage) and 3 (current)
  are not connected on this board.
- The board runs from 5 V on the power module connector J2, or from USB. Every other 5 V pin is an
  output.

> Warning: Never feed power into the 5 V pin of a JST-GH connector. Power the board through J2 or
> USB only.

## Cheat sheet

All connector cards on one A4 landscape sheet: <a href="../../../cheatsheets/MR-VMU-Tropic-cheatsheet.pdf">cheat sheet PDF</a>.

## References

- [MR-VMU-TROPIC board design and documentation](https://github.com/NXP-Robotics/MR-VMU-TROPIC)