Component: One Wire (Comms: Interface)

Author	Matrix Ltd
Version	1.4
Category	Comms: Interface

One Wire component

Low level routines for controlling or interacting with a standard one wire interface.

Detailed description

No detailed description exists yet for this component

Examples

Device Scanning

To get started with one wire devices it is often useful to collect the unique device serial number for each and every one wire device you are going to connect to your bus.

For example if you have a bus with two temperature sensors connected it is useful to know which sensor is which. Sensor A is monitoring temperature A and sensor B is monitoring temperature B. The only way to tell which is which is to use the serial number.

Here is a program that scans for devices on a one wire bus and outputs the device count and serial numbers using a LCD.

One Wire Device Scan LCD

Here is the same program but this time the device count and serial numbers are output using a UART such as on an Arduino or ESP32.

One Wire Device Scan Serial

To use the examples simply connect a single device to the one wire bus and make a note of the reported serial number.

This serial number can then be entered into the specific one wire component and used to ensure you are communicating with the device you think you are.

A pull up resistor of between 1K and 10K is required between the data I/O pin and VCC.

Further Examples

The One Wire component is a key building block required by a number of other components. Some of which are included below.

• DS1822 Temperature Sensor
• DS18B20 Temperature Sensor
• DS18S20 Temperature Sensor
• DS28E07 128 Byte EEPROM
• DS1990 iButton Unique 48-bit ID

Downloadable macro reference

	ReceiveByte
Receives a byte from the one wire bus a bit at a time
- BYTE	Return

	TransmitByte
Transmit a byte to the one wire bus a bit at a time
- BYTE	Command
- VOID	Return

	SkipROM
Performs a bus reset and the sends the SkipROM command byte
- VOID	Return

	BusReset
Issue a 'ping' on the bus. If there is at least one sensor on the bus then it will generate a presence pulse. Returns 0 if a presense pulse was detected Returns 1 no device was detected
[[File:]] -	Return

	MatchROM
Performs a reset followed by the MatchROM code and then the 8-bit ROM code.
- BYTE	FamilyCode
- BYTE	SerialNumber
- VOID	Return

	ScanBus
Scans the one wire bus to detect all connected devices. Returns the number of one wire devices found.
- BYTE	Return

	GetDeviceCount
Returns the number of devices found by the last ScanBus operation.
- BYTE	Return

	GetIDByte
Returns byte ectet of the 64-Bit lasered ROM code, 255 on error
- BYTE	Device
Device ID - Range: 0 - NumDevices - 1
- BYTE	ByteIndex
Index of the data byte. 0=FamilyCode, 1-6=Serial, 7=CRC
- BYTE	Return

	Initialise
Sets up the 1-Wire output pin ready for communications.
- VOID	Return

Property reference

	Properties
	One Wire Pin
I/O pin used to host one wire bus.
	Max Devices
Controls the maximum number of devices that can be detected during a ScanBus. For each additional device we require 8 bytes to store the ROM ID. Default: 8 = 64 Bytes of RAM
	6us Nops
	9us Nops
	10us Nops
	Nop Fiddle
	Connections
	Simulations
	API
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