Electronics > Microcontrollers

PIC UART Level Issue

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Joseph1:

--- Quote from: MIS42N on October 14, 2021, 08:54:10 am ---You didn't say if you have an oscilloscope. If you are using one of the cheap 3A buck converters, their output is quite noisy when the current draw is small. You should look there. You don't show any additional bypass capacitors on the SIM800L supply, it may pay to put more capacitance there, low ESR electrolytic and a ceramic. It seems people do have trouble with the power supply because of the very short 2A bursts of current. Also need a bypass on the FET gate to GND. You may have one but don't show it.

--- End quote ---

Yes I have an oscilloscope. BUt didn't try to capture some waveforms yet. I use cheap LM2596 buck modules Like these.
https://www.amazon.com/Lysignal-LM2596-Supply-Adjustable-Converter/dp/B074J4NXCM

I don't use any capacitors on the PCB except the 0.1uF ceramic cap to PIC micro.I guess the SIM800L modules have some 100uF cap & two ceramic caps on its board.DO I need additional caps for SIM800L module?

https://www.amazon.com/DAOKI-SIM800L-MicroSIM-Quad-Band-3-7-4-2V/dp/B08212SNVQ/ref=sr_1_6?crid=13FM1A01M2P14&dchild=1&keywords=sim800l&qid=1634486701&s=electronics&sr=1-6


Joseph1:

--- Quote from: DavidAlfa on October 14, 2021, 11:48:53 pm ---If your application doesn't really need 20MHz to comply the requirements, easy fix, it's 4V for 16MHz and 3V for 10MHz. (Datasheet page 136)
0.8x4VDD is 3.2V, still very close but might work. The best is to run it at 3.3V if possible.
Of course, the rest of the circuitry should be capable of working at such voltage.
Thats a prehistoric pic BTW.

--- End quote ---

For 9600bps I'm using internal 4Mhz oscillator.I'm doing testing on my original design (the 3V3 version).Most tries are ok.But sometimes in the noisy environment it misses the incoming phone number captured by the PIC..!!

oPossum:
Are you using the hardware UART? If so, what is the baud rate generator configuration. I suspect you have a more than 7% error on the bit rate. Should be under 2% for reliable operation.

Joseph1:

--- Quote from: oPossum on October 17, 2021, 04:55:08 pm ---Are you using the hardware UART? If so, what is the baud rate generator configuration. I suspect you have a more than 7% error on the bit rate. Should be under 2% for reliable operation.

--- End quote ---

I use hardware UART.
SPBRG =25(decimal)
oscillator =4Mhz internal osc

On SIM800L Init I dont send any baudrate commands in power up sequence.(Using the factory default ones).

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