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Diffstat (limited to 'Documentation/i2c/i2c-protocol.rst')
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1 files changed, 23 insertions, 22 deletions
diff --git a/Documentation/i2c/i2c-protocol.rst b/Documentation/i2c/i2c-protocol.rst index 2f8fcf671b2e..b2092f8f815d 100644 --- a/Documentation/i2c/i2c-protocol.rst +++ b/Documentation/i2c/i2c-protocol.rst @@ -1,26 +1,26 @@ -============ -I2C Protocol -============ +================ +The I2C Protocol +================ -This document describes the i2c protocol. Or will, when it is finished :-) +This document describes the I2C protocol. Or will, when it is finished :-) Key to symbols ============== =============== ============================================================= -S (1 bit) : Start bit -P (1 bit) : Stop bit -Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0. -A, NA (1 bit) : Accept and reverse accept bit. -Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to +S Start condition +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded as usual to get a 10 bit I2C address. -Comm (8 bits): Command byte, a data byte which often selects a register on +Comm (8 bits) Command byte, a data byte which often selects a register on the device. -Data (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh +Data (8 bits) A plain data byte. Sometimes, I write DataLow, DataHigh for 16 bit data. -Count (8 bits): A data byte containing the length of a block operation. +Count (8 bits) A data byte containing the length of a block operation. -[..]: Data sent by I2C device, as opposed to data sent by the +[..] Data sent by I2C device, as opposed to data sent by the host adapter. =============== ============================================================= @@ -28,7 +28,7 @@ Count (8 bits): A data byte containing the length of a block operation. Simple send transaction ======================= -This corresponds to i2c_master_send:: +Implemented by i2c_master_send():: S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P @@ -36,7 +36,7 @@ This corresponds to i2c_master_send:: Simple receive transaction ========================== -This corresponds to i2c_master_recv:: +Implemented by i2c_master_recv():: S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P @@ -44,11 +44,11 @@ This corresponds to i2c_master_recv:: Combined transactions ===================== -This corresponds to i2c_transfer +Implemented by i2c_transfer(). -They are just like the above transactions, but instead of a stop bit P -a start bit S is sent and the transaction continues. An example of -a byte read, followed by a byte write:: +They are just like the above transactions, but instead of a stop +condition P a start condition S is sent and the transaction continues. +An example of a byte read, followed by a byte write:: S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P @@ -57,7 +57,7 @@ Modified transactions ===================== The following modifications to the I2C protocol can also be generated by -setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they +setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they are usually only needed to work around device issues: I2C_M_IGNORE_NAK: @@ -77,8 +77,9 @@ I2C_M_NOSTART: S Addr Rd [A] [Data] NA Data [A] P If you set the I2C_M_NOSTART variable for the first partial message, - we do not generate Addr, but we do generate the startbit S. This will - probably confuse all other clients on your bus, so don't try this. + we do not generate Addr, but we do generate the start condition S. + This will probably confuse all other clients on your bus, so don't + try this. This is often used to gather transmits from multiple data buffers in system memory into something that appears as a single transfer to the |