Category:How to - i2c - Revision history

Sellis: Remove the Further Information section since the link dest has no content

2010-08-12T20:52:12Z

Remove the Further Information section since the link dest has no content

Sellis: Not supposed to include linux/i2c.h in userspace progs, I2C_SLAVE is also in linux/i2c-dev.h

2010-02-04T13:07:42Z

Not supposed to include linux/i2c.h in userspace progs, I2C_SLAVE is also in linux/i2c-dev.h

Sellis: Point to a simpler example, maybe more useful

2010-01-28T21:19:48Z

Point to a simpler example, maybe more useful

Sellis: Added a link to a level shifter explanation.

2010-01-15T14:02:31Z

Added a link to a level shifter explanation.

Sellis: Added reference to the schematics page

2010-01-14T18:19:11Z

Added reference to the schematics page

Sellis: spelling

2009-12-05T14:34:09Z

spelling

Sellis: Removed reference to board_overo.c. Anyone who would use this method doesn't need this instruction.

2009-11-24T11:17:00Z

Removed reference to board_overo.c. Anyone who would use this method doesn't need this instruction.

Sellis: Added a Sample code section and one link

2009-11-20T14:44:37Z

Added a Sample code section and one link

Sellis at 14:04, 19 October 2009

2009-10-19T14:04:40Z

Sellis at 13:58, 19 October 2009

2009-10-19T13:58:44Z

@@ Line 57: / Line 57: @@
   fh = open("/dev/i2c-3", O_RDWR);
-  /* tell the driver we want the device at address 0x20 */
+  /* tell the driver we want the device with address 0x20 on the I2C bus */
   ioctl(fh, I2C_SLAVE, 0x20);
@@ Line 69: / Line 69: @@
   close(fh);
 ==Sample code==

@@ Line 49: / Line 49: @@
   #include <sys/stat.h>
   #include <fcntl.h>
-  #include <linux/i2c.h> /* for I2C_SLAVE */
+  #include <linux/i2c-dev.h> /* for I2C_SLAVE */
     ...

@@ Line 76: / Line 76: @@
 ==Sample code==
-Here is a simple project showing how to use an overo to control some "smart" leds. It includes a schematic for the voltage level conversion of the I2C lines that's required.
+Here is a small project showing how to write Overo I2C userland code to communicate with an I/O expander as the slave device. It includes a schematic for the voltage level conversion of the I2C lines that's required.
-[http://github.com/scottellis/overo-blinkm Controlling BlinkM leds over I2C using a Gumstix Overo]
+[http://github.com/scottellis/overo-mcp23017 overo-mcp23017]
 [[Category:How_to_-_general]]

@@ Line 19: / Line 19: @@
 For many of the boards, pin 23 is SCL and pin 24 is SDA.
 The voltage levels are 1.8v, so a voltage level shifter is required to connect to 3.3 or 5 volt slave devices.
 The overo main board already has pullup resistors for SCL and SDA.
@@ Line 74: / Line 75: @@
 ==Sample code==
 [http://github.com/scottellis/overo-blinkm Controlling BlinkM leds over I2C using a Gumstix Overo]
 [[Category:How_to_-_general]]

@@ Line 11: / Line 11: @@
 There are several i2c buses available on the overo board.
-The one accessible from the 40 pin expansion board headers is i2c-3.
+The bus accessible from most of the 40 pin expansion board headers is i2c-3.
-Pin 23 is SCL and Pin 24 is SDA.
+Refer to the board [http://pubs.gumstix.com/boards/ schematics] to find whether the board you are using exposes the i2c lines.
 The voltage levels are 1.8v, so a voltage level shifter is required to connect to 3.3 or 5 volt slave devices.
@@ Line 45: / Line 49: @@
   #include <fcntl.h>
   #include <linux/i2c.h> /* for I2C_SLAVE */
-  ...
+   ...
-−
   int fh;
   uint8_t data[4];
-−
   fh = open("/dev/i2c-3", O_RDWR);
-−
   /* tell the driver we want the device at address 0x20 */
   ioctl(fh, I2C_SLAVE, 0x20);
-−
   /* write two bytes */
   data[0] = 0x05;
   data[1] = 0x08;
   write(fh, data, 2);
-−
   /* read 4 bytes */
   read(fh, data, 4);
-−
   close(fh);

@@ Line 5: / Line 5: @@
 The 2 wires are the SCL or clock wire and the SDL or data wire. The clock high to low transition is used to signal that the data wire has a stable 1/0 data value and that the receiver should shift this into the data results register. The clock line is high when the bus is idle. A special high to low transition on the clock line followed by a high to low transition on the data line signals the start of a message sequence. the end of a message sequence is a low to high transition in the data line followed by a low to high transition in the SCL line.  An important aspect of this communication standard is that each device is assigned a unique 7 bit address, (oh yea the 8th bit is the Read/write indicator to complete the byte). The device address is the first byte sent in any communication. Subsequent bytes of a message depend on the device you are talking to.
-Because of patents that have since expired, other companies had to use slightly differnet ways to do the same thing so a very similar serial communicatinos method called SPI uses 4 wires and another called TWI uses the same 2 wires.
+Because of patents that have since expired, other companies had to use slightly different ways to do the same thing so a very similar serial communications method called SPI uses 4 wires and another called TWI uses the same 2 wires.
 == I2C with Gumstix Overo ==
-There are several i2c busses available on the overo board.
+There are several i2c buses available on the overo board.
 The one accessible from the 40 pin expansion board headers is i2c-3.

@@ Line 21: / Line 21: @@
 The default gumstix kernels set the i2c-3 bus speed to 400 kHz.
-This can be changed to 100 kHz with a kernel command line parameter in u-boot
+This can be changed to 100 kHz with a kernel command line parameter in u-boot.
   i2c_bus=3,100
 The i2c-3 bus appears as a character device under /dev

← Older revision		Revision as of 14:44, 20 November 2009
Line 70:		Line 70:

	Another source of I2C information can be found [http://www.gumstix.net/wiki/index.php?title=I%C2%B2C here].		Another source of I2C information can be found [http://www.gumstix.net/wiki/index.php?title=I%C2%B2C here].
		+
		+	==Sample code==
		+
		+	[http://github.com/scottellis/overo-blinkm Controlling BlinkM leds over I2C using a Gumstix Overo]

	[[Category:How_to_-_general]]		[[Category:How_to_-_general]]

← Older revision		Revision as of 13:58, 19 October 2009
Line 6:		Line 6:

	Because of patents that have since expired, other companies had to use slightly differnet ways to do the same thing so a very similar serial communicatinos method called SPI uses 4 wires and another called TWI uses the same 2 wires.		Because of patents that have since expired, other companies had to use slightly differnet ways to do the same thing so a very similar serial communicatinos method called SPI uses 4 wires and another called TWI uses the same 2 wires.
		+
		+	== I2C with Gumstix Overo ==
		+
		+	There are several i2c busses available on the overo board.
		+
		+	The one accessible from the 40 pin expansion board headers is i2c-3.
		+
		+	Pin 23 is SCL and Pin 24 is SDA.
		+
		+	The voltage levels are 1.8v, requiring a voltage level translator to connect to 3.3 or 5 volt slave devices.
		+
		+	The overo main board already has pullup resistors for SCL and SDA.
		+
		+	The default gumstix kernels set the i2c-3 bus speed to 400 kHz.
		+
		+	This can be changed to 100 kHz with a kernel command line parameter in u-boot
		+
		+	i2c_bus=3,100
		+
		+	or by modifying ../git/arch/arm/mach-omap2/board-overo.c and rebuilding the kernel.
		+
		+	The i2c-3 bus appears as a character device under /dev
		+
		+	root@overo:/dev# ls -all i2c*
		+	crw-rw---- 1 root root 89, 1 Jan 1 2000 i2c-1
		+	crw-rw---- 1 root root 89, 3 Jan 1 2000 i2c-3
		+
		+	Programmers can access devices on the bus using standard unix file i/o.
		+
		+	You must set the slave address with an ioctl() call prior to communicating with a slave device.
		+
		+	The driver takes care of shifting the slave address one bit and appending the R/W bit in the first byte of the transfer.
		+
		+	Here's a C example minus any error checking.
		+
		+	...
		+	#include <stdint.h>
		+	#include <sys/types.h>
		+	#include <sys/stat.h>
		+	#include <fcntl.h>
		+	#include <linux/i2c.h> /* for I2C_SLAVE */
		+	...
		+
		+	int fh;
		+	uint8_t data[4];
		+
		+	slave_addr = 0x20;
		+
		+	fh = open("/dev/i2c-3", O_RDWR);
		+
		+	/* tell the driver we want the device at address 0x20 */
		+	ioctl(fh, I2C_SLAVE, 0x20);
		+
		+	/* write two bytes */
		+	data[0] = 0x05;
		+	data[1] = 0x08;
		+	write(fh, data, 2);
		+
		+	/* read 4 bytes */
		+	read(fh, data, 4);
		+
		+	close(fh);

	==Further information==		==Further information==