=================
stm32f401rc-rs485
=================

This page discusses issues unique to NuttX configurations for the
NuttX STM32F4-RS485 development board.

.. figure:: stm32f401rc_rs485.jpg
   :align: center

Board information
=================

This board was release on NuttX International Workshop 2023 and developed based on
STM32F401RCT6 microcontroller.

STM32F401RCT6 microcontroller features:
 - Arm 32-bit Cortex®-M4 CPU with FPU
 - 256 Kbytes of Flash memory
 - 64 Kbytes of SRAM
 - Serial wire debug (SWD) & JTAG interfaces
 - Up to 81 I/O ports with interrupt capability
 - Up to 11 communication interfaces
 - Up to 3 I2C interfaces
 - Up to 3 USARTs
 - Up to 4 SPIs
 - SDIO interface
 - USB 2.0 full-speed device/host/OTG controller with on-chip PHY


The board features:

- Digital I2C Temperature Sensor (TMP75)
- 2K bits (256x8) I2C EEPROM
- On-board RS485 Transceiver
- Two Analog Input Stages with Amplifier Buffer
- Two Analog Output Stages with Amplifier Buffer
- MicroSD Connector supporting 1 or 4-bit bus
- Four User LEDs
- Four User Buttons
- USB for DFU (Device Firmware Update) and USB device functionality, as well as powering the board
- Onboard voltage regulator from 5V to 3.3V
- SWD Pins for use as STLink (Pin header) and TC2030-IDC 6-Pin Tag-Connect Plug-of-Nails™ Connector
- Crystal for HS 8MHz
- Crystal for RTC 32.768KHz

Board documentation:
https://github.com/lucaszampar/NuttX_STM32F4_RS485_DevBoard

As F4 series have a USB DFuSe-capable BootROM [AN2606], the board can be flashed
via `dfu-util` over USB, or via `stm32flash` over UART without any debuggers.

LEDs
====

The STM32F4-RS485 has 4 software controllable LEDs.

=====  =====
LED    PINS
=====  =====
LED_1  PC0
LED_2  PC1
LED_4  PC2
LED_5  PC3
=====  =====

User Buttons
============

The STM32F4-RS485 has 4 user switches.

======= =====
SWITCH  PINS
======= =====
SWIO_1  PB13
SWIO_2  PB14
SWIO_3  PB15
SWIO_4  PC6
======= =====

UARTs
=====

The STM32F4-RS485 has 1 USART available for user.

USART2
------

========== =======
UART/USART PINS
========== =======
CTS        PA0
RTS        PA1
TX         PA2 [1]
RX         PA3
CK         PA4
========== =======

[1] Warning you make need to reverse RX/TX on some RS-232 converters

SDCard support
==============

The STM32F4-RS485 has 1 SDCard slot connected as below:

========== =====
SDIO       PINS
========== =====
SDIO_D0    PC8
SDIO_D1    PC9
SDIO_D2    PC10
SDIO_D3    PC11
SDIO_DK    PC12
========== =====

EEPROM
======

The STM32F4-RS485 development board has serial EEPROM HX24LC02B, with 2k bits (256x8) and internally
organized with 32 pages of 8 bytes each. It is connected through I2C as below:

====== =====
I2C    PINS
====== =====
SDA    PB7
SCL    PB8
====== =====

Users can enable EERPOM support on STM32F4-RS485 by following below configuration:

- Configure basic nsh::

       ./tools/configure.sh -l stm32f401rc-rs485:nsh

- Enable the following configs::

       CONFIG_DEV_ZERO=y
       CONFIG_EEPROM=y
       CONFIG_FS_PROCFS=y
       CONFIG_I2C=y
       CONFIG_I2C_EE_24XX=y
       CONFIG_STM32_I2C1=y

- Build and flash the STM32F4-RS485.
- Use dd command to write and read data from EEPROM as below::

       nsh> dd if=/dev/zero of=/dev/eeprom
       nsh: dd: write failed: 1
       nsh> dd if=/dev/console of=/dev/eeprom bs=1 count=4
       (type "Hello")
       nsh> dd if=/dev/eeprom of=/dev/console bs=4 count=1
       Hellonsh>

Temperature Sensor
==================

The STM32F4-RS485 development board has a temperature sensor TMP75 (TMP75AIDR) connected through I2C as below:

====== =====
I2C    PINS
====== =====
SDA    PB7
SCL    PB8
====== =====

RS485 Transceiver
=================

The STM32F4-RS485 development board has a half-duplex RS-485 transceiver, the BL3085B it is connected
through USART2 as below:

==========   =====
USART2       PINS
==========   =====
USART2_RX    RO
USART2_RTS   DE, /RE
SART2_RX     DI
==========   =====

A/D Converter
=============

The STM32F4-RS485 development board has two Analog to Digital converters with Amplifier Buffer (1COS724SR)
and connected as below:

======= =====
PWM     PINS
======= =====
PWM_1   PB6
PWM_2   PA6
======= =====

D/C Converter
=============

The STM32F4-RS485 development board has two Digital to Analog converters with Amplifier Buffer (1COS724SR)
and connected as below:

======= =====
ADC     PINS
======= =====
ADC_1   PA0
ADC_2   PA4
======= =====

Configurations
==============

Each stm32f401rc-rs485 configuration is maintained in a sub-directory and
can be selected as follow::

    tools/configure.sh stm32f401rc-rs485:<subdir>

Where <subdir> is one of the following:


Configuration Directories
-------------------------

nsh
---

Configures the NuttShell (nsh) located at apps/examples/nsh. This
configuration enables a serial console on UART2.

sdcard
------

Configures the NuttShell (nsh) and enables SD card support.
The stm32f401rc-rs485 has an onboard microSD slot that should
be automatically registered as the block device /dev/mmcsd0 when
an SD card is present.  The SD card can then be mounted by the
NSH commands::

       nsh> mount -t procfs /proc
       nsh> mount -t vfat /dev/mmcsd0 /mnt