UART half-duplex WeAct STM32F411 - working only when ST Link V2 is connected

[dacair]

Hi there,
I am working on a joystick and using a Winwing F-16 Viper grip that sends button status through a half-duplex 230400 baud rate connection. STM32 sends 0x0A then the grip responds with 8 bytes,
My issue is that it only works when ST Link V2 is connected.
I have:
PA9 as TX/RX pin added external 10k pull-up resistor
NRST - added external 10k pull-up resistor
The three wires Data, 3v3 and GND on half-duplex are ~120mm long. There's a PS/2 connected with a ~50mm cable inside the grip, then my PS/2 connector with a ~70mm 3 wire cable

I connected a digital analyzer and while not working properly, it is visible it cannot even send 0xA0 fully.

I need some advice - what can I do more to make it work?
If required I can share additional info, code or pictures.

Thanks,

 

[dacair]

Hei there,
Is there anyone can help with some hints?
Or did I miss to provide some information?

 

[Martaine2005]

Hi, I know nothing about programming.
But if it works when the ST link is connected, surely the code/program has not been uploaded to the microcontroller?.

 

[dacair]

Hi, I know nothing about programming.
But if it works when the ST link is connected, surely the code/program has not been uploaded to the microcontroller?.

It seems it is related to electronics.
The MCU sends just a byte 0x0A. I put the osciloscope probes and uart decoder and can show some good full messages but then only shows part of this byte - usually the beginning of the 8 bits. ( 0x0A = 01010000 ) it would send ... 010000 or even the first 4 bits 0x0101 --- then looses sync with the baud rate ...

 

[Martaine2005]

There must be something 'common’ when the ST is in circuit. Maybe a GND or other connection that is required?.
Can you post your schematic here?

 

[dacair]

Hi Martaine,
I'm sorry I'm so late with the answer, it was crazy busy last week ...
Please see attached picture.
The board is a WeAct STM32F411CEU
** Red wires - are supplies and signals from/to strain gauges ( HX711 ) - that works fine
** Half Duplex UART
* Green, Black, White - are the connections to the grip . On the grip side ( inside ) there are PS/2 connectors ( the grip has a male connector and my cable is female connector ). All three wires (WH, BK , GN ) are ~70mm long
* Initially the WH (GND) and BK (3V3) were soldered where the Red wires GND,3V3 are but, I moved it closer to USB ... . It actually improved a bit so now it connects but in some certain cases is disconnecting during normal use.

Can you please advice - what can I do to resolve this issue?