SMAART Wire Communication Interface

SMAART Wire Communication Interface

1. Communication Protocol

   • Only the host initiates communication. Before communication begins, all the daisy-chained devices are in  transparent mode. In this mode, all the host operations are sequentially transferred to all the devices in the chain. The devices in the chain cannot communicate with each other with the exception of the address initialize command. After initialization, the devices in the chain are in one of the following four modes: • wait for a command from the host (default mode) • transmit the device data back to the host • transmit the commands from the host to the subsequent device in the chain • transmit the data from the subsequent device back to the host
   • Calibration Phase
     • The calibration phase is the first phase of every communication, and consists of the host sending 10-bits.
     • Pull the line low in the beginning to notify each device that the host is initiating  communication.
     • The host transmits calibration sequence 55h at the desired communication baud rate. The connected devices receive this calibration byte and calculate the baud rate to communicate with the host. This  calibration byte is sent at the beginning of every operation; therefore, each address or command operation can be performed at a different baud rate. 
   • Command and Address Phase
     • The second phase of every communication is the command and address phase.
     • The values of the bits in this phase determine the format and structure of subsequent phases in the communication operation.
     • Global or Individual (G/nI) Bit
       • The G/nI bit indicates if the communication is a global operation (intended for more than one device) or individual   (intended for only one device).
       • All command operations are global; therefore, for command operations, always set the G/nI bit to 1.
       • For read and write address operations to multiple devices in the daisy chain simultaneously, set this bit to 1. To access an individual device, set the G/nI bit to 0.
       • During global operation, the host sets the address portion of the command to the maximum address required to  perform the communication. For example, to perform a write to the high-limit register of all devices between  addresses 1h to 5h in the daisy chain, set the G/nI bit to 1 and the address field to 5h. For individual accesses, set the address field to the desired device address. 
     • Read/Write (R/nW) Bit
       • The R/nW bit indicates whether the operation is read or write to the TMP107 device.
     • Command or Address (C/nA) Bit
       • The C/nA bit indicates whether the current communication is a command operation or address operation. The  C/nA bit = 1 indicates a command operation. The codes for specific commands in the TMP107 are listed in Table 2. Codes other than those listed in Table 2 are reserved for factory use only.
       • The C/nA bit = 0 indicates an address operation. The five bits following the C/nA bit (A4 to A0) are the address  bits of the device or devices that the host intends to communicate with in the chain, as shown in Figure 20. 
   • Register Pointer Phase
     • The register pointer phase is provided only if the communication is an address operation.
     • This phase of the  communication shows the register pointer of the device that the host in going to write to or read from.
     • The pointer  byte has special identification code bits, as shown in Figure 21. 
   • Data Phase
     • The data phase is the last phase of communication. Every register location consists of two words of data. Therefore, this last phase of communication consists of at least two bytes of data with the least significant byte sent first, followed by the most significant byte.
     • For a write operation, the host sends data to the device or devices at the specified register pointer location. 
     • For a read operation, the specified device or devices respond back with the data from the location specified in the register pointer phase. 
     • Depending on the value of G/nI bit in the command and address phase, the data in this phase are either written  to a targeted individual device, or to multiple devices in the daisy-chain. 

2. SMAART Wire Operations

   • Command Operations
     • Address Initialize
     • Last Device Poll
     • Global Software Reset
   • Address Operations
     • Individual Write
     • Individual Read
     • Global Write
     • Global Read

3. Device Functional Modes

   • Continuous-Conversion Mode
   • Shutdown Mode
   • One-Shot Mode

4. EEPROM

   • Programming
   • EEPROM Operations
     • EEPROM Unlock
     • EEPROM Lock
     • EEPROM Programming
     • EEPROM Acquire or Read

5. Register Map

   • Temperature Register
   • Configuration Register
   • EEPROM n Register
   • Die ID Register
   • limit
     • High Limit 1 Register
     • Low Limit 1 Register
     • High Limit 2 Register
     • Low Limit 2 Register