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SARTHAK KELAPURE
SARTHAK KELAPURE
Associate III
December 19, 2017
Question

Max Payload for US915 and extra UART

  • December 19, 2017
  • 2 replies
  • 1761 views
Posted on December 19, 2017 at 15:26

I have two queries for anyone who can help me,

1)What is the maximum payload for US915_HYBRID, SF7, 125kHz BW for LoRa?

2)I need an extra UART on stm32l072cz LoRa discovery board. Can anyone help with this.

Please help.

Thanks in advance

#b-l072z-lrwan1
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2 replies

Andrew Neil
Andrew Neil
Super User
December 19, 2017
Posted on December 19, 2017 at 16:18

1)What is the maximum payload for US915_HYBRID, SF7, 125kHz BW for LoRa?

You can look that up in the LoRa specifications; specifically, the Regional Parameters document.

https://www.lora-alliance.org/lorawan-for-developers

 

I need an extra UART on stm32l072cz LoRa discovery board

See: 

https://community.st.com/community/stm32-community/blog/2017/04/05/lora-discovery-kit?commentID=4355&et=blogs.comment.created#comment-4355

 

If there's not sufficient on-board, then you have the standard two possibilities:

  1. Implement a soft UART;
  2. Add external hardware.
A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
Tesla DeLorean
Tesla DeLorean
Guru
December 19, 2017
Posted on December 19, 2017 at 16:40

The radio supports up to 255 bytes when suitable configured, by default I think it is 64 bytes, so consider ways to packetize data, or compress current data.

USART options are limited

PA2/PA3 USART2(LPUART1)

PA9/PA10 USART1

PA13/PA14 LPUART1 (SWD)

PA0 USART4_TX (DEBUG TELEMETRY)

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SARTHAK KELAPURE
SARTHAK KELAPUREAuthor
Associate III
December 20, 2017
Posted on December 20, 2017 at 09:29

Why am I not able to use PB6/PB7 and PA9/PA10 togetherly??

Andrew Neil
Andrew Neil
Super User
December 20, 2017
Posted on December 20, 2017 at 09:52

It is important that you learn to read the board schematic, and the chip datasheet.

Look at the B-L072Z-LRWAN1 schematic:

  • PB7 is connected to LD4 (red);
  • PB6

     is connected to LD3 (blue).

So, if you want to use them for UART comms, you'll have to disconnect those LEDs.

The board's User Manual (as well as the schematic) tell you how to do that.

Look at Table 16. STM32L072xxx pin definition in the Datasheet:

  • PB6/7 have USART1 as Alternate Function

    , with PB6=TX, PB7=RX;

  • PA9/10 also 

    have the same USART1 as Alternate Function, with PA9=TX, PA10=RX.

So you could use PB6/PA10 or PA9/PB7, subject to pin availability on the board - see above.

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
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