HydraFW UART guide

HydraFW Bus UART (Universal Asynchronous Receiver/Transmitter)

This guide is updated towards firmware release HydraFW v0.11 and later

Bus: UART, MIDI (universal asynchronous receiver transmitter).
Connections: two pins (RX/TX) and ground.
Output types: 3.3volt normal output, or open drain
(pull-up/pull-down resistors integrated in MCU or external).
Pull-up resistors: required for open collector output mode (2K – 10K).
Pull-up/down resistors Integrated in MCU: Between 30 to 50K (Typical 40K).
Maximum Voltage: 5.5volts (5volt safe).

UART is also known as the common PC serial port.
The PC serial port operates at full RS232 voltage levels
(-13volts to +13volts) though, which are not compatible with the HydraBus.

Protocol configuration syntax description:

• show Show UART parameters or show pins Show pins used in this mode

• device with parameter 1 or 2 to choose UART device (1 or 2)

• speed with integer baudrate value (support k, m suffix or no suffix)

  • UART1 Baudrate from 1281 and up to 10.5M
  • UART2 Baudrate from 640 and up to 5.25M
  • Standard UART baudrate: 2400, 4800, 9600, 19200, 38400, 57600, 115200, 31250

• parity with parameter none or even or odd for parity value

• stop-bits with parameter 1 or 2 for number of stop bits

• bridge to enter USB <-> UART mode

• trigger configures the trigger mode

• scan tries to calculate the baudrate (See baudrate detection)

• exit to exit UART mode

Note default value for device 1 or 2: 
For device 1 (UART1):
> uart device 1
Note: UART parameters have been reset to default values.
Device: UART1
Speed: 9600 bps
Parity: none
Stop bits: 1

For device 2 (UART2):
> uart device 2
Note: UART parameters have been reset to default values.
Device: UART2
Speed: 9600 bps
Parity: none
Stop bits: 1

Configuration options:

Hardware Informations:

uart1> show pins
TX: PA9
RX: PA10

uart2> show pins
TX: PA2
RX: PA3

Protocol configuration example:

Configuration of UART1 9600bauds 8bits data, 1stop, no parity:

> uart device 1
Note: UART parameters have been reset to default values.
Device: UART1
Speed: 9600 bps
Parity: none
Stop bits: 1

Protocol interaction syntax description:

Bus interaction commands

Protocol interaction example usage UART1 write:

uart1> 0xFF 0 1 0x80 0x55 0xAA 0xFF 0x11:4
WRITE: 0xFF 0x00 0x01 0x80 0x55 0xAA 0xFF 0x11 0x11 0x11 0x11

Bridge mode

Hydrabus can be used as a USB to UART bridge with the bridge command :

> uart 
Device: UART1
Speed: 9600 bps
Parity: none
Stop bits: 1
uart1> bridge 
Interrupt by pressing user button.

Baud rate detection

Since cb2ebea9f694a344fee28b2baf4e160f7066dcf2, Hydrabus can automatically detect the baudrate on a UART line.

In order to do that, connect the device TX line to PC6, and run the scan command :

uart1> scan
Estimated baudrate : 57712

The baudrate detection waits for at least 10 bytes sent to the UART, then measures the shortest transition to calculate the baudrate. This means that you need to make sure that bytes are sent on the target UART in order to measure the signal.

UART baudrate and error

Example of baudrates and related error:

Extreme baudrate example:

Baudrate	10,500,000	8,400,000	6,000,000	5,250,000	4,000,000
Final baudrate	10,500,000	8,400,000	6,000,000	5,250,000	4,000,000
Error %	0.000	0.000	0.000	0.000	0.000

Baudrate	3,000,000	2,000,000	2,500,000	1,000,000	921,600
Final baudrate	3,000,000	2,000,000	2,470,588	1,000,000	923,076
Error %	0.000	0.000	1.190	0.000	0.160

Standard baudrate example:

Baudrate	460,800	250,000	230,400	115,200	57,600	38,400
Final baudrate	461538	250,000	230,136	115,226	57,613	38,408
Error %	0.160	0.000	0.110	0.030	0.030	0.030

baudrate from 33,600 to 2400 bauds 0% error

Additional information about baudrate error:

• https://www.robotroom.com/Asynchronous-Serial-Communication-2.html
• Important information:

Therefore, to be fair, each device is only allowed to be less than 2.5% in error, to ensure that the total difference in timing between devices is less than 5%. To provide a safer margin, Atmel recommends a 2% error or less per device.

Additional informations about UART

For more details on UARTprotocol see: http://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter

Tests & informations from Philippe Teuwen Wiki: https://wiki.yobi.be/index.php/HydraNFC#HydraBus_UART

Recommended USB High Speed to UART interface (for real-time data input/output using High Speed UART)

STLINK-V3SET USB2.0 HS interface (USB CDC up to 10.5MBaud)

Support HydraBus v1 UART1(PA10/USART1_RX & PA9/USART1_TX) up to 10.5Mbaud

• See https://github.com/hydrabus/hydrafw/wiki/Getting-Started-with-HydraBus-and-STM32CubeIDE#2-2-connect-stlink-v3set-swd--swo--usart1txrx-to-hydrabus-v1-for-advanced-debuggingtraces

FTDI USB2.0HS interface (USB CDC support up to 8.4MBaud)

• FTDI interface C232HM-DDHSL-0 (3.3V Output Level, 0.5M cable) See https://wiki.yobi.be/index.php/HydraNFC#HydraBus_UART

• I recommend to use FTDI C32HM-DDHSL-0 cable with 6MegaBaud (8N1) settings on both side (tested with HydraBus uart1 bridge & FTDI C232HM-DDHSL-0)

• Datasheet: https://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_C232HD_UART_CABLE.pdf

  • UART FTDI C232HM-DDHSL-0 to HydraBus connection:

    C232HM-DDHSL-0 Pin	HydraBus Pin
    Orange ADBUS0 TX(Pin2)	PA10 / USART1_RX
    Yellow ADBUS1 RX(Pin3)	PA9 / USART1_TX
    Black GND (Pin10)	GND (near PA9)

  
  • Note1: FTDI C232HM-DDHSL-0 Baudrate of 8.4MBaud is possible when setting the FTDI C232HM-DDHSL-0 to any value greater or equal to 6.3MBauds.
  • Note2: FTDI C232HM-DDHSL-0 Baudrate of 8.4MBaud DutyCycle is 46.4% / 53.6% or the reverse so up to +/-3.6% error/variation but still works with HydraBus configured @8.4MBauds.
  • Warning: FTDI C232HM-DDHSL-0 Baudrate values like 6.2MBauds, 6.6MBauds, 7.1MBauds, 7.7MBauds set the FTDI Baudrate to 115.2KBauds.

• FTDI C232HM-EDHSL-0 (5V Output Level, 0.5M cable) => Not tested