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[SOLVED] UART prints "????" when kept on hold on reset

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Raady Here

Raady Here

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Hi,

I have configured UART, sending and receiving data is absolutely fine.
But it prints '?' mark continuously (see attachment) if it is kept in
1. 'hold on reset ' condition
2. while dumping the code to processor
3. press reset button

I just want to know is it a common phenomenon or a problem so that corrections can be made with my hardware or software.

MPLAB 8.8/dspic30f5011

Regards,
Raady.

1.jpg
 

Hi,

I think, there is noise in your hardware.
1) check your hardware for any loose connection or dry solder
2) Add some electrolyte filter capacitor between VCC and GND.

Hope this is help you
 

Vcc and GND w.r.t RS232 IC or any thing else ? or where exactly ?

Can we observe that noise through oscilloscope ?
 

I have been using ports for UART and programming chip separately.
 
Last edited:

Hi,

One 100uF/16V electrolyte capacitor connect near RS232 IC and
one 47uF/16 electrolyte capacitor connect near micro. You can also connect one 0.1uF in paraller with 47uF capacitor near micro.

Regards,
 
?'s ascii value is 0x3F that is 0b0011 1111 with start and stop bit 0 1111 1100 1.. so you are getting a square wave on that pin at that time check out for it... Try to embed a parity bit on your communication and see...
 

g_shyam1682 said:
Hi,

One 100uF/16V electrolyte capacitor connect near RS232 IC and
one 47uF/16 electrolyte capacitor connect near micro. You can also connect one 0.1uF in paraller with 47uF capacitor near micro.

Regards,
Click to expand...

Is it possible to measure the noise at the port using an oscilloscope ?
 

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