ATtiny1604 Alternate Pins For Serial

Other Hardware 3rd Party Boards
1

I am trying to build a project using an ATtiny1604.

I need to use PWM (to control a servo) and TWI (to talk to a transducer) and Serial (for debug oputput and command entry) but the default pin assignments clash.

Looking at data sheet, there are no alternative pin assignments for TWI SCL or SDA on my device so that prevents my using TCA0 PWM signal output on WO0 and WO1.

I found a reference to using Serial.swap(); just after the Serial.begin(); statement and I was hoping this would use the alternate pins for TxD, RxD (PA1, PA2) so that the default TxD, Rxd pins (PB2, PB3) would be released.

If this were the case, I could then use WO2 or the alternate WO0 pin for the PWM output.

I have a stripped down version to illustrate my problem.

How do you cause Serial to use the alternate pins on an ATtiny1604?

// ATtiny1604_Serial_Test
// Target ATtiny1604

#include <Arduino.h>
/* ATtiny1604 / ARDUINO Pins
 *                          _____
 *                  VDD   1|*    |14  GND
 * (nSS)  (AIN4) PA4  0~  2|     |13  10~ PA3 (AIN3)(SCK)(EXTCLK)
 *        (AIN5) PA5  1~  3|     |12  9   PA2 (AIN2)(MISO)
 * (DAC)  (AIN6) PA6  2   4|     |11  8   PA1 (AIN1)(MOSI)
 *        (AIN7) PA7  3   5|     |10  11  PA0 (nRESET/UPDI)
 * (RXD) (TOSC1) PB3  4   6|     |9   7~  PB0 (AIN11)(SCL)
 * (TXD) (TOSC2) PB2  5~  7|_____|8   6~  PB1 (AIN10)(SDA)
*/
/* Alternate pins 
Pin Name  Other     ADC0  AC0   USART0  SPIO  TWI0  TCA0  TCB0  CCL

 1  VDD
 2  PA4             AIN4        XDIR(*) SS          WO4         LUT0-OUT
 3  PA5             AIN5  OUT                       WO5   WO
 4  PA6             AIN6  AINN0
 5  PA7             AIN7  AINP0                                 LUT1-OUT
 6  PB3                         RxD                 WO0(*)
 7  PB2   EVOUT1                TxD                 WO2
 8  PB1             AIN10       XCK           SDA   WO1
 9  PB0             AIN11       XDIR          SCL   WO0
 10 PA0 RESET/UPDI  AIN0                                        LUT0-IN0
 11 PA1             AIN1        TxD(*)  MOSI                    LUT0-IN1
 12 PA2 EVOUT0      AIN2        RxD(*)  MISO                    LUT0-IN2
 13 PA3 EXTCLK      AIN3        XCK(*)  SCK         WO3
 14 GND
*/

#define Serial_BAUD 19200			

// declare functions here
void system_init();

void setup() {
  // put your setup code here, to run once:
  system_init();
  Serial.begin(Serial_BAUD);
  Serial.swap();
/*							The default TxD, RxD pins are PB2, PB3 
//							I was hoping that Serial.swap() would use the alternate pins for 
//							TxD, RxD would be used (PA1, PA2) but this is not the case.
*/
  Serial.println(F("\r\nStart"));
  delay(500);
}

void loop() {
  // put your main code here, to run repeatedly:
  Serial.println(F("Loop"));
  delay(500);
}

// put function definitions here:
// Initialization routines 
void mcu_init()							// MCU initialization 
{
	/* On AVR devices all peripherals are enable from power on reset, this
	 * disables all peripherals to save power. Driver shall enable
	 * peripheral if used.
	*/

	// Set all PORT A pins to low power mode and input disabled 
	for (uint8_t i = 0; i < 8; i++) {                                   			// PA0 - PA7
		uint8_t *port_pin_ctrl = ((uint8_t *)&PORTA + 0x10 + i);				
		*port_pin_ctrl |= (1 << PORT_PULLUPEN_bp); 									// define pull up 
		*port_pin_ctrl = (*port_pin_ctrl & ~PORT_ISC_gm) | PORT_ISC_INTDISABLE_gc; 	// disable input sensing
	}

    // Set all PORT B pins to low power mode and input disabled 
	for (uint8_t i = 0; i < 4; i++) {                                   			// PB0 - PB3 on ATtiny1604
		uint8_t *port_pin_ctrl = ((uint8_t *)&PORTB + 0x10 + i);				
		*port_pin_ctrl |= (1 << PORT_PULLUPEN_bp); 									// define pull up 
		*port_pin_ctrl = (*port_pin_ctrl & ~PORT_ISC_gm) | PORT_ISC_INTDISABLE_gc; 	// disable input sensing
	}
}

void system_init(){							// system initialization 
	mcu_init();
}

I can work round the issue by using SoftwareSerial and specifying the pins I want to use but this seems 'cluncky' when I think I should be able to use Serial (and the USART).

2

You have swap and begin in the wrong order.

try this

  Serial.swap();
  Serial.begin(Serial_BAUD);

you get your TX then on PA1

O, and compliments on the careful formatting of your question, with a trimmed down problem demonstrator sketch. That's how you get help fast.

3

Many thanks - that was the solution.

I was lead astray by this item which would have you place Serial.swap() after Serial.begin()

https://arduino-esp8266.readthedocs.io/en/latest/reference.html

Best regards

4

I like that approach less, as I suspect then you have to open serial first on the ports you do not want to use and only after that closing those ports and opening the alternates you do want to use.

Megatinycore let's you choose the ports you want to use first and only then opens those straight away.