Max Payload for US915 and extra UART

[SARTHAK KELAPURE]

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

[Andrew Neil]

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.

[Tesla DeLorean]

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)

[SARTHAK KELAPURE]

Posted on December 20, 2017 at 09:29

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

[Andrew Neil]

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.

[Andrew Neil]

Posted on December 20, 2017 at 09:54

Neil.Andrew wrote:

if you want to use [PB6,7] for UART comms, you'll have to disconnect those LEDs.

and, of course, disable any software that tries to use them as LEDs!

[SARTHAK KELAPURE]

Posted on December 20, 2017 at 10:13

I don't think LEDs will be a problem. My solution to this is initializing PA9/10 when I need them and using PB6/7 when I need them, what do you think, will this work?

[Andrew Neil]

Posted on December 20, 2017 at 10:17

You haven't said what you're trying to achieve by that - so impossible to say whether it would work or not!

[SARTHAK KELAPURE]

Posted on December 20, 2017 at 10:23

I have connected a device1 to PORTA 9/10 and need it to get data1, while

I have connected a device2 to PORTB 6/7 and need it to get data2.

While getting data1, I shall initialize AF6-USART1 on PORTA 9/10 and de-initialize after my work is done, and

While getting data2, I shall initialize AF0-USART1 on PORTB 6/7 and

 de-initialize after my work is done.

I hope it is clear

[Andrew Neil]

Posted on December 20, 2017 at 10:35

So you are effectively making a 'changeover' switch to route the two devices (one at a time) to the one UART.

In principle, that should work.

In practice, it assumes that nothing (important) comes from the 'disconnected' device while you're not listening to it...