patch-2.3.34 linux/Documentation/i2c/smbus-protocol

• Lines: 128
• Date: Thu Dec 16 13:59:38 1999
• Orig file: v2.3.33/linux/Documentation/i2c/smbus-protocol
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.33/linux/Documentation/i2c/smbus-protocol linux/Documentation/i2c/smbus-protocol
@@ -0,0 +1,127 @@
+Some adapters understand only the SMBus (System Management Bus) protocol,
+which is a subset from the I2C protocol. Fortunately, many devices use
+only the same subset, which makes it possible to put them on an SMBus.
+If you write a driver for some I2C device, please try to use the SMBus
+commands if at all possible (if the device uses only that subset of the
+I2C protocol). This makes it possible to use the device driver on both
+SMBus adapters and I2C adapters (the SMBus command set is automatically
+translated to I2C on I2C adapters, but plain I2C commands can not be
+handled at all on a pure SMBus adapter).
+
+Below is a list of SMBus commands.
+
+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 
+                get a 10 bit I2C address.
+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
+                for 16 bit data.
+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 host adapter.
+
+
+SMBus Write Quick
+=================
+
+This sends a single byte to the device, at the place of the Rd/Wr bit.
+There is no equivalent Read Quick command.
+
+A Addr Rd/Wr [A] P
+
+
+SMBus Read Byte
+===============
+
+This reads a single byte from a device, without specifying a device
+register. Some devices are so simple that this interface is enough; for
+others, it is a shorthand if you want to read the same register as in
+the previous SMBus command.
+
+S Addr Rd [A] [Data] NA P
+
+
+SMBus Write Byte
+================
+
+This is the reverse of Read Byte: it sends a single byte to a device.
+See Read Byte for more information.
+
+S Addr Wr [A] Data NA P
+
+
+SMBus Read Byte Data
+====================
+
+This reads a single byte from a device, from a designated register.
+The register is specified through the Comm byte.
+
+S Addr Wr [A] Comm [A] S Addr Rd [A] [Data] NA P
+
+
+SMBus Read Word Data
+====================
+
+This command is very like Read Byte Data; again, data is read from a
+device, from a designated register that is specified through the Comm
+byte. But this time, the data is a complete word (16 bits).
+
+S Addr Wr [A] Comm [A] S Addr Rd [A] [DataLow] A [DataHigh] NA P
+
+
+SMBus Write Byte Data
+=====================
+
+This writes a single byte to a device, to a designated register. The
+register is specified through the Comm byte. This is the opposite of
+the Read Byte Data command.
+
+S Addr Wr [A] Comm [A] Data [A] P
+
+
+SMBus Write Word Data
+=====================
+
+This is the opposite operation of the Read Word Data command. 16 bits
+of data is read from a device, from a designated register that is 
+specified through the Comm byte. 
+
+S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P
+
+
+SMBus Process Call
+==================
+
+This command selects a device register (through the Comm byte), sends
+16 bits of data to it, and reads 16 bits of data in return.
+
+S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] 
+                             S Addr Rd [A] [DataLow] A [DataHigh] NA P
+
+
+SMBus Block Read
+================
+
+This command reads a block of upto 32 bytes from a device, from a 
+designated register that is specified through the Comm byte. The amount
+of data is specified by the device in the Count byte.
+
+S Addr Wr [A] Comm [A] 
+           S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P
+
+
+SMBus Block Write
+=================
+
+The opposite of the Block Read command, this writes upto 32 bytes to 
+a device, to a designated register that is specified through the
+Comm byte. The amount of data is specified in the Count byte.
+
+S Addr Wr [A] Comm [A] Count [A] Data [A] Data [A] ... [A] Data [A] P