About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / i2c / i2c-protocol




Custom Search

Based on kernel version 3.15.4. Page generated on 2014-07-07 09:03 EST.

1	This document describes the i2c protocol. Or will, when it is finished :-)
2	
3	Key to symbols
4	==============
5	
6	S     (1 bit) : Start bit
7	P     (1 bit) : Stop bit
8	Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0.
9	A, NA (1 bit) : Accept and reverse accept bit.
10	Addr  (7 bits): I2C 7 bit address. Note that this can be expanded as usual to
11	                get a 10 bit I2C address.
12	Comm  (8 bits): Command byte, a data byte which often selects a register on
13	                the device.
14	Data  (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh
15	                for 16 bit data.
16	Count (8 bits): A data byte containing the length of a block operation.
17	
18	[..]: Data sent by I2C device, as opposed to data sent by the host adapter.
19	
20	
21	Simple send transaction
22	======================
23	
24	This corresponds to i2c_master_send.
25	
26	  S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P
27	
28	
29	Simple receive transaction
30	===========================
31	
32	This corresponds to i2c_master_recv
33	
34	  S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
35	
36	
37	Combined transactions
38	====================
39	
40	This corresponds to i2c_transfer
41	
42	They are just like the above transactions, but instead of a stop bit P
43	a start bit S is sent and the transaction continues. An example of
44	a byte read, followed by a byte write:
45	
46	  S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P
47	
48	
49	Modified transactions
50	=====================
51	
52	The following modifications to the I2C protocol can also be generated by
53	setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they
54	are usually only needed to work around device issues:
55	
56	I2C_M_IGNORE_NAK:
57	    Normally message is interrupted immediately if there is [NA] from the
58	    client. Setting this flag treats any [NA] as [A], and all of
59	    message is sent.
60	    These messages may still fail to SCL lo->hi timeout.
61	
62	I2C_M_NO_RD_ACK:
63	    In a read message, master A/NA bit is skipped.
64	
65	I2C_M_NOSTART:
66	    In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some
67	    point. For example, setting I2C_M_NOSTART on the second partial message
68	    generates something like:
69	      S Addr Rd [A] [Data] NA Data [A] P
70	    If you set the I2C_M_NOSTART variable for the first partial message,
71	    we do not generate Addr, but we do generate the startbit S. This will
72	    probably confuse all other clients on your bus, so don't try this.
73	
74	    This is often used to gather transmits from multiple data buffers in
75	    system memory into something that appears as a single transfer to the
76	    I2C device but may also be used between direction changes by some
77	    rare devices.
78	
79	I2C_M_REV_DIR_ADDR:
80	    This toggles the Rd/Wr flag. That is, if you want to do a write, but
81	    need to emit an Rd instead of a Wr, or vice versa, you set this
82	    flag. For example:
83	      S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P
84	
85	I2C_M_STOP:
86	    Force a stop condition (P) after the message. Some I2C related protocols
87	    like SCCB require that. Normally, you really don't want to get interrupted
88	    between the messages of one transfer.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.