1-Wire Core

This core allows the board to act as a 1-Wire master to communicate with Dallas/Maxim 1-Wire buses. This core contains only 1 16-bit register and works by doing 1-wire read/write ops 8-bits at a time.

Register Map

Offset	Bits	Access	Description
0x0	15-13	Read/Write	LUN select (0-7)
	12	Read Only	Busy
	12	Write Only	Special CMD Enable
	11-8	Read/Write	Bytes to read
	7-0	Read/Write	Read data, write data, or special CMD

Special Commands

Command	Description
8'b0000_0000	no-op
8'b1xxx_xxxx	Initiate 1-wire reset, presence returned in bit 0. Short detect return in bit 1.
8'b01xx_xxxx	1-bit write, bit written is bit 0

Bytes to Read

Value	Read size
0x0	Read disabled
0x1	1 byte
0x2	2 bytes
...	...
0xd	13 bytes
0xe	1 bit (returned in data bit 7)
0xf	2 bits (returned in data bits 6 and 7)

This example below is for talking to a Maxim DS401 chip with a unique serial number. Since all 1-Wire devices contain a unique serial, this should be applicable for most devices.

#include <stdio.h>
#include <unistd.h>

#define OW_ADDR 0x58

unsigned char ow_read8()
{
	unsigned short ret;

	sbuslock();
	ret = sbus_peek16(OW_ADDR);
	sbusunlock();

//	printf("Ret: 0x%x\n", ret);

	// Check for busy bit
	if(ret & (1 << 12)) {
		printf("Busy... retrying\n");
		usleep(1);
		ret = ow_read8();
	}

	return (char)ret & 0xff;
}

unsigned short ow_write8(unsigned short val)
{
	sbuslock();
	sbus_poke16(OW_ADDR, val);
	sbusunlock();
}

int main()
{
	unsigned short ret;
	unsigned short crc;
	unsigned short fcode;
	unsigned long long serial = 0;
	int i;

	// Send reset
	ow_write8(0x1080);

	// Detect presence of 1-wire device
	ret = ow_read8();

	if(!(ret & (1 << 0))) {
		fprintf(stderr, "No presence detected on the one wire bus\n");
		return;
	}

	// Send Read ROM command 0x33, and request 8 bytes
	ow_write8(0x833);

	fcode = ow_read8();

	// Read in 48 bits of the serial
	for(i=0; i < 6; i++) {
		serial |= ((unsigned long long) (ow_read8() & 0xff) << (8*i));
	}
	crc = ow_read8();;

	printf("serial: 0x%llx\n", serial);
}