Electrical – STM32 USART Receive Binary Number

cstm32uart

I'm new to embedded systems so apologies if this is a stupid question.

I am trying to implement a binary counter in the form of 8 LEDs. I want to send an 8-bit binary number through USART and have the 8 LEDs display the number (led off if bit is 0, led on when bit is 1).

What would be the best method to do this?

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I want to send an 8-bit binary number through USART and have the 8 LED's display the number (led off if bit is 0, led on when bit is 1). What would be the best method to do this?

The built-in UART already decodes the serial signal into bytes. Put another way, the hardware delivers you the byte you want directly. Your question then comes down to how to drive 8 LEDs from the 8 separate bits of a byte somewhere in the processor.

The easiest solution is to use 8 output pins. It would be particularly easy if these are all driven by the same output port register internally. In that case, you simply write the byte to the port register.

If the output lines are scattered among different port registers, then in the worst case you set each bit individually. Test the LSB of the input byte, then set or clear the port bit for that LED. Then test bit 1 and set or clear the port bit for the next LED, etc.

The simplest electrically is to drive each LED directly from its output pin:

If the LED drops 2.1 V (typical for common green), then it will have about 5 mA thru it when the digital signal is high. That will be plenty bright enough with a modern LED to easily see in a typical office environment.

Related Solutions

Electronic – UART on the atmega328. Dataregister on the USART (UCSR0A) status never set on

I don't see where you put the correct F_CPU definition, which is mandatory for setbaud.h.

You also have to define the BAUD macro to use UBRR(L|H)_VALUE, like this:

#define F_CPU 1e6       // 1Mhz clock
#include <avr/io.h>
#include <util/delay.h>

void initUSART(void) {
 #define BAUD 9600
 #include <util/setbaud.h> 
 UBRR0H = UBRRH_VALUE;
 UBRR0L = UBRRL_VALUE;
// ...
}

You can also calculate the UBRRnx values with this site. The values depend on your clock speed and the prescaler setting. At the default configuration it is simply one, so it is not used.

And don't forget the pull-up resistors (about 10K ohm) at the TX/RX lines.

I hope this helps.

Electronic – STM32 USART with DMA — which interrupts to use

You can configure DMA to work in cyclic mode, and with reasonable big buffer you can pull characters as often as you want with simple poll function. Just store index of last character retrieved and use DMA register to check how many characters it has to receive until roll over (AFAIR register has NDTR in its name), and process characters received since last call, then update index of last character retrieved.

Described DMA usage makes your poll independent from context you call it from as long as you prevent preemption. Then you can use RX interrupt to trigger poll call(s), or you can do it in other context (for example with some periodic events).

This is generally efficient if frames are long enough, baudrate is big and interrupt latency is bigger than reception time of single char.

But if data is received slow enough you can get away with processing it char by char current way, and using DMA may be overkill.

As @Chris Stratton pointed you can also just set DMA for single transmission, and wait long enough, change protocol or use other signal as "end of transmission" - and then process frame in DMA buffer.

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Related Solutions

Electronic – UART on the atmega328. Dataregister on the USART (UCSR0A) status never set on

Electronic – STM32 USART with DMA — which interrupts to use

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