RS485 example for at tiny 3216

[coderatchance]

Hello all!

Trying to test the RS485 between two attiny3216, but no example around ?
So far I am looking at the [Arduino RS485 library] (https://docs.arduino.cc/libraries/arduinors485/ )

Connecting the ST4E1216 part.

  Serial.swap(0);

The pin RXD and TXD, 6 and 7 pin are respectively connected to the R and D of the transceiver, however, I am not sure to what pins should the RE and DE (enable) be connected to? Since the ST4e1216 has automatic direction control, therefore, I guess may be relevant?

Printed out the pins of the serial:
PIN_SERIAL_RX: 1
PIN_SERIAL_TX: 0
PIN_SERIAL_XCK: 2
PIN_SERIAL_XDIR: 3

What are these numbers? Thought I would find those number in the Port Function Multiplexing, but nothing...

Any ideas?

Indeed, it would be much easier to start with an example, do we have one where I can find more information how to get going ?

Any comments, etc. are more than welcome!

Best.

[mechatroniks-git]

That library is likely not compatible with megatinycore. You might be able to ask them to add support.

No need for a library here, it's just serial communication with an additional pin to assert while transmitting. Typically you tie DE and /RE together and to a gpio. Then before you transmit serial, set it high and pull it low when you are done.

The proper way would be to wait until serial buffer is empty before pulling the pin low. You can use Serial.availableForWrite() to check.

If you want to be able to check for collision, then don't tie /RE to DE, just pull /RE to ground and leave it there. Then you will read back everything you transmit. Then you have to compare what was sent to what was received to determine collision. Usually a good idea for multi-drop. Should not be needed for just 2 devices, if the other device has good manners.

[coderatchance]

Thanks for the explanation!
You are right the Arduino could add the support especially with regard to the XDIR pin.
Apparently, listing of the pins , such as the XDIR, etc. is only meant for the libraries to know what pins are used, if I am understanding this correctly, more here: https://github.com/SpenceKonde/megaTinyCore/blob/master/megaavr/extras/Ref_Serial.md

It would be wonderful and much less complicated if the XDIR could be used?

But is not this explained here : "On tinyAVR parts with more than 8 pins, the two mapping options for Serial are PB2, PB3, PB1, PB0 and PA1, PA2, PA3, PA4 for TX, RX, XCK, XDIR." ? Should not then the XDIR be used on the PB0 and PA4? Anyway, I am using those ports for something else :( will have to try what you are suggesting. I guess the /RE and DE pins are arbitrarily selected on the uC?

Best.

[mechatroniks-git]

Ah, looks like the hardware natively supports RS485, so does the core. It's all done for you if you use XDIR pin and enable SERIAL_RS485

[coderatchance]

Would you share me an example?

BTW I am not sure how to print what I am sending.
For example, I am using a different serials, namely on for the RS485 swap(0) and the other for the Serial print swap(1).

[mechatroniks-git]

Not able to give an example, but use the arduino examples and just modify the begin command.

Serial.begin(115200,(SERIAL_RS485));

Make sure you are using the right pins on 3216. Not sure which device package you are using, but USART0 is not using pins 6 or 7 on either package.

For example pins 7&8 are used as primary for SOIC. Use pin swap for the alternate pins (1) on 17&18.

Since there is only 1 UART on this device, and you are connecting it to RS485, you will need a usb to rs485 to snoop the communication

[coderatchance]

Regarding the connection on 3216 swap(0) I am connecting the following:

tiny: -------> transceiver:
PB2 = TXD -> R (digital output)
PB3 = RXD -> D (digital input)
PB0 = XDIR -> (/RE + DE) connected together

not sure about the PB1 , XCK, where, if at all, is this connected to the transceiver?

A->A
B->B

Sometimes this is confusing, because it used as twisted pair, which may imply A->B, B->A !

Is this ok? With this code I cannot get it to work...

//sending 
void setup() {

  pinMode(green, OUTPUT);
  pinMode(blue, OUTPUT);

  Serial.swap(0);

  Serial.begin(9600, (SERIAL_HALF_DUPLEX | SERIAL_RS485) );

  if (Serial.available()) {
    blinkLed(blue);
  }
  blinkLed(green);
}

void loop() {

  if (Serial.availableForWrite()) {
    for (byte i = 0; i < 100; i++) {
      Serial.write(45);
    }
    blinkLed(blue);
  }

}

// receiving
void setup() {

  pinMode(green, OUTPUT);
  pinMode(blue, OUTPUT);

  Serial.swap(0);
  
  Serial.begin(9600, (SERIAL_HALF_DUPLEX | SERIAL_RS485) );
  
  if (Serial.available()) {
    blinkLed(blue);
  }
}

Best.

PS Maybe should the software serial be used to test out ? https://www.gammon.com.au/forum/?id=11428

[coderatchance]

[mechatroniks-git]

I like the 2-series devices when using serial, then I have a debug port. Check out the ATtiny1624

[coderatchance]

Thanks, I was actually wondering what is the difference between the 1624 and 1626. I guess in number of pins, ports...
Indeed, it is much easier to get the new part... I guess with two UARTS it will possible to preview the serial output on one UART, while on the other the RS485 will be used?

BTW is it possible to put the XDIR elsewhere or is this set in stone?

Best.

[coderatchance]

OK, finally got to the end, it actually works!

In my case, the trick was in manually setting the /RE, DE, and the Serial.flush().

But, there are still questions :

• if either is used, works, I am wondering does the SERIAL_RS485 enables the function of XDIR ?

//Serial.begin(115200);
Serial.begin(115200, SERIAL_RS485);

[coderatchance]

Is there a way to test out if the port is working properly?
For example, the Serial(0) works ok. The voltage on both pins is 5V, which is as well my VCC.

While the Serial(1), does not, however, the port PA2 shows 5V, while on port PA1 is mV, rather 0V,
indeed, I guess I cannot measure the signal in this way, hence I am asking how to actually use the PA1 and e.g. turn on the led or whatever, for example, I can turn on the led easily on the PA2.

In addition, I have tried to swap this serial to the PC2 and PC1 port and I get the same phenomena, for example, I can easy turn on the led on the PC2, while I cannot get the PC1 do anything.
So, how to tackle this :)

[coderatchance]

Would that analogRead(14); provide the reading on the PA1 port? Of course when the pinMode(14, INPUT);
Does this make any sense?
Anyway, I guess I can put 5V or ground on the input?

[hmeijdam]

it is doing exactly what you tell it.
Serial.swap(0) is setting the port back to the default position.

Do this and you will get both UARTS outputting on their alternate pin locations PA1 and PC2

void setup() {
 Serial.swap(1);
 Serial1.swap(1);
 Serial.begin(115200);
 Serial1.begin(9600);
}

void loop() {
Serial.println("This is UART0");
Serial1.println("And I am UART1");
delay(1000);
}

[hmeijdam]

Or if you want to print to two serial devices on a part with one UART use an alternating schedule.

void setup() {
}

void loop() {
  Serial.begin(115200);
  Serial.println("This is UART0 on default pin with 115200 baud");
  Serial.end();
  delay(1000);
  Serial.swap(1); // set to alternate
  Serial.begin(9600);
  Serial.println("This is UART0 on alternate pin with 9600 baud");
  Serial.end();
  Serial.swap(0); // set back to default pins
  delay(1000);
}

[coderatchance]

Thanks! I have solved the problem, it was not ironically about the software, but the hardware, namely tiny was apparently not working, hence I was thinking about how to test the ports... anyway, this is solved, time to move on and test both UARTS at the same time!