API Description

This module allows one to use MRAA's UART support in order to interact with Dallas 1-wire compliant devices on a 1-wire bus. It makes use of the UART for timing purposes. The principle of operation is described here: https://www.maximintegrated.com/en/app-notes/index.mvp/id/214

It is important the you use a UART with CMOS/TTL level voltages (3.3v/5v) RX and TX lines. DO NOT use standard RS232 level voltages, or you are going to have a bad day.

In addition, a diode should be placed across the RX and TX lines like so:

-| U| A| TX—|<–+ R| | T| RX----—o-----—o 1-wire data bus -|

The diode on TX is a 1N4148 (cheap and common), with the cathode connected to TX, and the anode connected to RX and the rest of the 1-wire data line.

    uart_ow = mraa_uart_ow_init(0);
    if (uart_ow == NULL) {
        fprintf(stderr, "Failed to initialize UART OW\n");
        mraa_deinit();
        return EXIT_FAILURE;
    }
    // Reset the ow bus and see if anything is present
    status = mraa_uart_ow_reset(uart_ow);
    if (status == MRAA_SUCCESS) {
        fprintf(stdout, "Reset succeeded, device(s) detected!\n");
    } else {
        goto err_exit;
    }
    fprintf(stdout, "Looking for devices...\n");
    /*
     * we are essentially doing a binary tree search through the 64
     * bit address space.  id is modified during this search, and will
     * be set to the valid rom code for each device found.
     *
     * start the search from scratch
     */
    status = mraa_uart_ow_rom_search(uart_ow, 1, id);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }
    while (status == MRAA_SUCCESS) {
        /* The first byte (id[0]]) is the device type (family) code.
         * The last byte (id[7]) is the rom code CRC value.  The
         * intervening bytes (id[1]-id[6]) are the unique 48 bit
         * device ID.
         */
        fprintf(stdout, "Device %02d Type 0x%02x ID %02x%02x%02x%02x%02x%02x CRC 0x%02x\n", count,
                id[0], id[6], id[5], id[4], id[3], id[2], id[1], id[7]);
        count++;
        // continue the search with start argument set to 0
        status = mraa_uart_ow_rom_search(uart_ow, 0, id);
    }
    /* stop uart_ow */
    mraa_uart_ow_stop(uart_ow);

Go to the source code of this file.

Data Structures
struct	_mraa_uart_ow

Functions
mraa_uart_ow_context	mraa_uart_ow_init (int uart)

mraa_uart_ow_context	mraa_uart_ow_init_raw (const char *path)

const char *	mraa_uart_ow_get_dev_path (mraa_uart_ow_context dev)

mraa_result_t	mraa_uart_ow_stop (mraa_uart_ow_context dev)

int	mraa_uart_ow_read_byte (mraa_uart_ow_context dev)

int	mraa_uart_ow_write_byte (mraa_uart_ow_context dev, uint8_t byte)

int	mraa_uart_ow_bit (mraa_uart_ow_context dev, uint8_t bit)

mraa_result_t	mraa_uart_ow_reset (mraa_uart_ow_context dev)

mraa_result_t	mraa_uart_ow_rom_search (mraa_uart_ow_context dev, mraa_boolean_t start, uint8_t *id)

mraa_result_t	mraa_uart_ow_command (mraa_uart_ow_context dev, uint8_t command, uint8_t *id)

uint8_t	mraa_uart_ow_crc8 (uint8_t *buffer, uint16_t length)

Macros
#define	MRAA_UART_OW_ROMCODE_SIZE 8

Typedefs
typedef struct _mraa_uart_ow *	mraa_uart_ow_context

Enumerations
enum	mraa_uart_ow_rom_cmd_t { MRAA_UART_OW_CMD_READ_ROM = 0x33, MRAA_UART_OW_CMD_MATCH_ROM = 0x55, MRAA_UART_OW_CMD_SKIP_ROM = 0xcc, MRAA_UART_OW_CMD_SEARCH_ROM_ALARM = 0xec, MRAA_UART_OW_CMD_SEARCH_ROM = 0xf0 }

Function Documentation

mraa_uart_ow_context mraa_uart_ow_init ( int uart )

Initialise uart_ow_context, uses UART board mapping

Parameters

uart	the index of the uart set to use

Returns: uart_ow context or NULL

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mraa_uart_ow_context mraa_uart_ow_init_raw ( const char * path )

Initialise a raw uart_ow_context. No board setup.

Parameters

path	for example "/dev/ttyS0"

Returns: uart_ow context or NULL

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const char* mraa_uart_ow_get_dev_path ( mraa_uart_ow_context dev )

Get char pointer with tty device path within Linux For example. Could point to "/dev/ttyS0"

Parameters

dev	uart_ow context

Returns: char pointer of device path

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mraa_result_t mraa_uart_ow_stop ( mraa_uart_ow_context dev )

Destroy a mraa_uart_ow_context

Parameters

dev	uart_ow context

Returns: mraa_result_t

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int mraa_uart_ow_read_byte ( mraa_uart_ow_context dev )

Read a byte from the 1-wire bus

Parameters

dev	uart_ow context

Returns: the byte read or -1 for error

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int mraa_uart_ow_write_byte	(	mraa_uart_ow_context	dev,
		uint8_t	byte
	)

Write a byte to a 1-wire bus

Parameters

dev	uart_ow context
byte	the byte to write to the bus

Returns: the byte read back during the time slot or -1 for error

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int mraa_uart_ow_bit	(	mraa_uart_ow_context	dev,
		uint8_t	bit
	)

Write a bit to a 1-wire bus and read a bit corresponding to the time slot back. This is possible due to the way we wired the TX and RX together with a diode, forming a loopback.

Parameters

dev	uart_ow context
bit	the bit to write to the bus

Returns: the bit read back during the time slot or -1 for error

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mraa_result_t mraa_uart_ow_reset ( mraa_uart_ow_context dev )

Send a reset pulse to the 1-wire bus and test for device presence

Parameters

dev	uart_ow context

Returns: one of the mraa_result_t values

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mraa_result_t mraa_uart_ow_rom_search	(	mraa_uart_ow_context	dev,
		mraa_boolean_t	start,
		uint8_t *	id
	)

Begin a rom code search of the 1-wire bus. This function implements the 1-wire search algorithm. See the uart_ow.c example for an idea on how to use this function to identify all devices present on the bus.

Parameters

dev	uart_ow context
start	true to start a new search from scratch, false to continue an existing search
id	the 8-byte rom code id of the current matched device when a device is found

Returns: one of the mraa_result_t values

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mraa_result_t mraa_uart_ow_command	(	mraa_uart_ow_context	dev,
		uint8_t	command,
		uint8_t *	id
	)

Send a command byte to a device on the 1-wire bus

Parameters

dev	uart_ow context
command	the command byte to send
id	the rom code id of the device to receive the command, NULL for all devices on the bus

Returns: one of the mraa_result_t values

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uint8_t mraa_uart_ow_crc8	(	uint8_t *	buffer,
		uint16_t	length
	)

Perform a Dallas 1-wire compliant CRC8 computation on a buffer

Parameters

buffer	the buffer containing the data
length	the length of the buffer

Returns: the computed CRC

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Macro Definition Documentation

#define MRAA_UART_OW_ROMCODE_SIZE 8

8 bytes (64 bits) for a device rom code

Typedef Documentation

typedef struct _mraa_uart_ow * mraa_uart_ow_context

for now, we simply use the normal MRAA UART context

Enumeration Type Documentation

enum mraa_uart_ow_rom_cmd_t

UART One Wire ROM related Command bytes

Enumerator
MRAA_UART_OW_CMD_READ_ROM	read rom, when only one device on bus
MRAA_UART_OW_CMD_MATCH_ROM	match a specific rom code
MRAA_UART_OW_CMD_SKIP_ROM	skip match/search rom
MRAA_UART_OW_CMD_SEARCH_ROM_ALARM	search all roms in alarm state
MRAA_UART_OW_CMD_SEARCH_ROM	search all rom codes

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API Description

Data Structures

Functions

Macros

Typedefs

Enumerations

Function Documentation

Macro Definition Documentation

Typedef Documentation

Enumeration Type Documentation