Some adapters understand only the SMBus (System Management Bus) protocol,which is a subset from the I2C protocol. Fortunately, many devices useonly 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 SMBuscommands if at all possible (if the device uses only that subset of theI2C protocol). This makes it possible to use the device driver on bothSMBus adapters and I2C adapters (the SMBus command set is automaticallytranslated to I2C on I2C adapters, but plain I2C commands can not behandled at all on a pure SMBus adapter).Below is a list of SMBus commands.Key to symbols==============S     (1 bit) : Start bitP     (1 bit) : Stop bitRd/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 bit to the device, at the place of the Rd/Wr bit.There is no equivalent Read Quick command.A Addr Rd/Wr [A] PSMBus Read Byte===============This reads a single byte from a device, without specifying a deviceregister. Some devices are so simple that this interface is enough; forothers, it is a shorthand if you want to read the same register as inthe previous SMBus command.S Addr Rd [A] [Data] NA PSMBus 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 PSMBus 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 PSMBus Read Word Data====================This command is very like Read Byte Data; again, data is read from adevice, from a designated register that is specified through the Commbyte. 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 PSMBus Write Byte Data=====================This writes a single byte to a device, to a designated register. Theregister is specified through the Comm byte. This is the opposite ofthe Read Byte Data command.S Addr Wr [A] Comm [A] Data [A] PSMBus Write Word Data=====================This is the opposite operation of the Read Word Data command. 16 bitsof 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] PSMBus Process Call==================This command selects a device register (through the Comm byte), sends16 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 PSMBus 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 amountof 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 PSMBus 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 theComm 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