ThroughSerial

ThroughSerial

Medium: Hardware/Software Serial port | Pins used: 1 or 2

With ThroughSerial strategy, PJON can run through a software or hardware Serial port working out-of-the-box with many Arduino compatible serial transceivers, like RS485 or radio modules like HC-12 (HCMODU0054). Take a look at the video introduction for a brief showcase of its features. It complies with TSDL v2.1.

Why PJON over Serial?

Serial communication is fast and reliable but it is often useless without all the features PJON contains. ThroughSerial has been developed to enable PJON communication through a serial data link. Adding PJON on top of Serial it is possible to leverage of the PJON protocol layer features like acknowledge, addressing, multiplexing, packet handling, 8 or 32-bit CRC and traffic control.

Being impossible to detect or avoid collisions over a serial port, ThroughSerial has been developed primarily to be used in master-slave mode. ThroughSerial in multi-master mode, being unable to detect or avoid collisions, operates using the slotted ALOHA medium access method. Of all contention based random multiple access methods, slotted ALOHA, which maximum data throughput is only 36.8% of the available bandwidth, is one of the least efficient and should not be applied in networks where many devices often need to arbitrarily transmit data.

Configuration

Before including PJON.h it is possible to configure ThroughSerial using predefined constants:

Constant	Purpose	Supported value
TS_BYTE_TIME_OUT	Maximum byte response time-out	Duration in microseconds (50000 by default)
TS_RESPONSE_TIME_OUT	Maximum response time-out	Duration in microseconds (10000 by default)
TS_BACK_OFF_DEGREE	Maximum back-off exponential degree	Numeric value (4 by default)
TS_MAX_ATTEMPTS	Maximum transmission attempts	Numeric value (20 by default)

Pass the ThroughSerial type as PJON template parameter to instantiate a PJON object ready to communicate through this Strategy.

PJON<ThroughSerial> bus;

Call the begin method on the Serial or SoftwareSerial object you want to use for PJON communication and pass it to the set_serial method:

#include <PJON.h>

PJON<ThroughSerial> bus;

void setup() {
  Serial.begin(9600);
  bus.strategy.set_serial(&Serial);
}

For a simple use with RS485 serial modules a transmission enable pin setter has been added:

bus.strategy.set_enable_RS485_pin(11);

If separate enable setters are needed use:

// Set RS485 reception enable pin
bus.strategy.set_RS485_rxe_pin(11);
// Set RS485 transmission enable pin
bus.strategy.set_RS485_txe_pin(12);

In some cases it may be required to add a delay before disabling the RS485 pins txe and or rxe:

// Set RS485 txe/rxe pins disable delay in milliseconds
bus.strategy.set_RS485_delay(1);

See RS485-Blink and RS485-AsyncAck examples.

HC-12 wireless module supports both synchronous and asynchronous acknowledgement, see HC-12-Blink, HC-12-SendAndReceive, HC-12-LocalChat and HC-12-AsyncAck examples.

All the other necessary information is present in the general Documentation.

Known issues

• Being PJON not an interrupt driven, its communication can be affected and potentially disrupted by long delays added in the user's sketch. Try to reduce as possible the interval between every receive call.

Safety warning

In all cases, when installing or maintaining a PJON network, extreme care must be taken to avoid any danger. Before any practical test or hardware purchase for a wireless ThroughSerial radio setup, compliance with government requirements and regulations must be ensured.