Functions for maintaining the proper data line state. More...

Functions
void	SDI12::forceHold ()
	Set line state to SDI12_HOLDING. More...

void	SDI12::forceListen ()
	Set line state to SDI12_LISTENING. More...

Detailed Description

Functions for maintaining the proper data line state.

The Arduino is responsible for managing communication with the sensors. Since all the data transfer happens on the same line, the state of the data line is very important.

Per the SDI-12 specification, the voltage ranges for SDI-12 are:

When the pin is in the SDI12_HOLDING state, it is holding the line LOW so that interference does not unintentionally wake the sensors up. The interrupt is disabled for the dataPin, because we are not expecting any SDI-12 traffic.
In the SDI12_TRANSMITTING state, we would like exclusive control of the Arduino, so we shut off all interrupts, and vary the voltage of the dataPin in order to wake up and send commands to the sensor.
In the SDI12_LISTENING state, we are waiting for a sensor to respond, so we drop the voltage level to LOW and relinquish control (INPUT).
If we would like to disable all SDI-12 functionality, then we set the system to the SDI12_DISABLED state, removing the interrupt associated with the dataPin. For predictability, we set the pin to a LOW level high impedance state (INPUT).

Summarized in a table:

State	Interrupts	Pin Mode	Pin Level
SDI12_DISABLED	Pin Disable	INPUT	—
SDI12_ENABLED	Pin Disable	INPUT	—
SDI12_HOLDING	Pin Disable	OUTPUT	LOW
SDI12_TRANSMITTING	All/Pin Disable	OUTPUT	VARYING
SDI12_LISTENING	All Enable	INPUT	—

Sequencing

Generally, this is acceptable. HOLDING --> TRANSMITTING --> LISTENING --> TRANSMITTING --> LISTENING -->

If you have interference, you should force a hold, using forceHold(); HOLDING --> TRANSMITTING --> LISTENING --> done reading, forceHold(); HOLDING

See also: For a detailed explanation of interrupts see interrupts_page

Function Documentation

◆ forceHold()

void SDI12::forceHold ( )

Set line state to SDI12_HOLDING.

A public function which forces the line into a "holding" state. This is generally unneeded, but for deployments where interference is an issue, it should be used after all expected bytes have been returned from the sensor.

◆ forceListen()

void SDI12::forceListen ( )

Set line state to SDI12_LISTENING.

A public function which forces the line into a "listening" state. This may be needed for implementing a slave-side device, which should relinquish control of the data line when not transmitting.