UART not receiving data when sent through putty

[rahul7515]

i am using stm3210e-eval board which has stm32f103zgt6 mcu and i trying to send data on its uart but i am not able to receive any. i am trying to receiving it through blocking mode 

uint8_t rx[10];
HAL_UART_Receive(&huart2,rx,1,HAL_MAX_DELAY);
HAL_Delay(1000);

now this is the code and i have put the breakpoint on HAL_Delay so that as soon as data is received it will next stop on HAL_Delay but it does not break it stays stuck into uart function there and is not data getting received. I am using FL232RL to send data from putty to mcu pins of uart i can ensure that data is being sent from putty because when i hit enter onto putty i can see the green led getting blinked with each send of data but i am not getting anything over there but i can send data from mcu to putty i can see that clearly so what is happening

PS: i have double checked the baud rate it correctly set and the uart is transmit and receive mode i have tried changing it to receive mode only but that doesn't help 

image of putty configuration for sending the data

[Andrew Neil]

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@rahul7515 wrote:

i am using stm3210e-eval board

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So the same as here:

https://community.st.com/t5/stm32-mcus-products/uart-sending-some-else-data-and-not-as-intended/td-p/686958

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@rahul7515 wrote:

. I am using FL232RL to send data from putty to mcu pins of uart

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As noted in that previous thread, the stm3210e-eval board has RS232 Transceivers connected to the MCU's UART pins:

https://community.st.com/t5/stm32-mcus-products/uart-sending-some-else-data-and-not-as-intended/m-p/687059/highlight/true#M252609

So you'll need to disconnect those before connecting your FL232RL ...

[rahul7515]

well i cannot just disconnect those because they are on board and soldered and i am not sending the data onto rs232 pin but the actual MCU pins given as header PA2 and 3 or PA9,10

[Andrew Neil]

Are there not any links or solder bridges to disconnect them?

You can't just connect the FL232RL output - because it will be shorted to the ST3232C output!

Or just get yourself a USB-to-RS232 converter, and connect to the DE9 

EDIT:

Or use a Nucleo-F103RB instead ?

https://www.st.com/en/evaluation-tools/nucleo-f103rb.html

[Andrew Neil]

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@Andrew Neil wrote:

Are there not any links or solder bridges to disconnect them?

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Yes, there are zero-ohm links on every output from the ST3232C chips  to the MCU input pins:

[rahul7515]

well i can't just desolder those miniature smd resistors

[rahul7515]

changing the board is no solution and besides even if it is connected to its out why does that matter i am directly giving my input their it should directly go to the mcu 

[Andrew Neil]

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@rahul7515 wrote:

i can't just desolder those miniature smd resistors

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Of course you can - that's exactly why they're there!

All you need is to break the connection - you don't need to be careful about not damaging the "resistors".

Alternatively, again, get yourself a USB-to-RS232 converter (or two; or a double), and connect to the DE9(s):

[Andrew Neil]

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@rahul7515 wrote:

 even if it is connected to its out why does that matter

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Think about it:

If the ST3232C output is giving a '1', and your FL232RL output tries to give a '0' you are shorting the '1' and '0' together - that's not going to work!

Similarly, If the ST3232C output is giving a '0', and your FL232RL output tries to give a '1' you are again shorting a '1' and '0' together - that's not going to work!

It's a general principle of electronics that you can't just* wire two outputs together.

It's fine to have one output driving two (or more) inputs (so long as you don't overload the output) - that's why the transmit from your MCU works.

* there are special cases of outputs specifically designed for this - but you can't just do it without "special measures"

#ShortingOutputs

[SofLit]

Hello @rahul7515 ,

As stated by @Andrew Neil there is a short circuit between RS232 transceiver output going to UART_Rx and your FL232RL bridge output!

It's a very basic concept in digital electronics: don't connect two outputs directly together. For that either ORing the outputs or using open-drain config which is not possible in your case.

So you don't have any solution than disconnecting ST3232C by removing the adequate 0 ohm resistors.