1 ================
2 The I2C Protocol
3 ================
4
5 This document is an overview of the basic I2C
6 APIs to perform them.
7
8 Key to symbols
9 ==============
10
11 =============== ==============================
12 S Start condition
13 P Stop condition
14 Rd/Wr (1 bit) Read/Write bit. Rd equals 1, W
15 A, NA (1 bit) Acknowledge (ACK) and Not Ackn
16 Addr (7 bits) I2C 7 bit address. Note that t
17 get a 10 bit I2C address.
18 Data (8 bits) A plain data byte.
19
20 [..] Data sent by I2C device, as op
21 host adapter.
22 =============== ==============================
23
24
25 Simple send transaction
26 =======================
27
28 Implemented by i2c_master_send()::
29
30 S Addr Wr [A] Data [A] Data [A] ... [A] Data
31
32
33 Simple receive transaction
34 ==========================
35
36 Implemented by i2c_master_recv()::
37
38 S Addr Rd [A] [Data] A [Data] A ... A [Data]
39
40
41 Combined transactions
42 =====================
43
44 Implemented by i2c_transfer().
45
46 They are just like the above transactions, but
47 condition P a start condition S is sent and th
48 An example of a byte read, followed by a byte
49
50 S Addr Rd [A] [Data] NA S Addr Wr [A] Data [
51
52
53 Modified transactions
54 =====================
55
56 The following modifications to the I2C protoco
57 setting these flags for I2C messages. With the
58 are usually only needed to work around device
59
60 I2C_M_IGNORE_NAK:
61 Normally message is interrupted immediatel
62 client. Setting this flag treats any [NA]
63 message is sent.
64 These messages may still fail to SCL lo->h
65
66 I2C_M_NO_RD_ACK:
67 In a read message, master A/NA bit is skip
68
69 I2C_M_NOSTART:
70 In a combined transaction, no 'S Addr Wr/R
71 point. For example, setting I2C_M_NOSTART
72 generates something like::
73
74 S Addr Rd [A] [Data] NA Data [A] P
75
76 If you set the I2C_M_NOSTART variable for
77 we do not generate Addr, but we do generat
78 This will probably confuse all other clien
79 try this.
80
81 This is often used to gather transmits fro
82 system memory into something that appears
83 I2C device but may also be used between di
84 rare devices.
85
86 I2C_M_REV_DIR_ADDR:
87 This toggles the Rd/Wr flag. That is, if y
88 need to emit an Rd instead of a Wr, or vic
89 flag. For example::
90
91 S Addr Rd [A] Data [A] Data [A] ... [A]
92
93 I2C_M_STOP:
94 Force a stop condition (P) after the messa
95 like SCCB require that. Normally, you real
96 between the messages of one transfer.
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