The TMP127-Q1 operates as a peripheral and is compatible with SPI or MICROWIRE bus specifications. Data is clocked out on the falling edge of the serial clock (SCLK), while data is clocked in on the rising edge of SCLK. A complete transmit/receive communication will consist of 32 serial clocks. The first 16 clocks comprise the transmit phase of communication from the Device ID or Temperature Register, while the second 16 clocks are the receive phase to the Configuration Register. There is no issue using 8-bit SPI with the 16-bit interface as long as the CS remains low during the transaction. Mode transitions through writes to the configuration register will occur on the 16th rising clock edge during the 16-bit write.

Two modes of SPI communication are supported:

• Mode 0:
  • CPOL = 0
  • CPHA = 0
• Mode 3:
  • CPOL = 1
  • CPHA = 1

When CS is high, SIO will be in low-impedance tri-state. The user should take the chip select (CS) low to initiate communication. This should not be done when SCLK is changing from a low to high state. When CS is low, the serial I/O pin (SIO) will transmit the first bit of data. The controller can then read this bit with the rising edge of SCLK. The remainder of the data will be clocked out by the falling edge of SCLK. CS can be taken high at any time during the transmit phase. If CS is brought low in the middle of a conversion, the TMP127-Q1 will complete the conversion and the output shift register will be updated after CS is brought back high.

The receive phase of a communication starts after 16 SCLK periods. CS can remain low as long as required. After 32 SCLK rising edges, the TMP127-Q1 will take control of the SIO pin and be ready for another read write cycle. The TMP127-Q1 will read the data available on the SIO line on the rising edge of the serial clock. The last 8 bits of the configuration register are the Mode[7:0] bits and place the device into shutdown or continuous conversion mode. The receive phase can last up to 16 SCLK periods. Only the following operation codes will affect the TMP127-Q1 and any other codes placed into the Mode[7:0] field will be ignored

• 00 hex for continuous conversion
• FF hex for shutdown

Figure 8-2 shows an overview of the communication protocol.

After start-up or upon entering continuous mode, 200 ms must pass for a conversion to complete before the TMP127-Q1 transmits accurate temperature data.

The following communication can be used to determine the Manufacturer's/Device ID and then immediately place the part into continuous conversion mode. With CS continuously low:

• Read 16 bits of temperature data
• Write 16 bits of data commanding Shutdown Mode(00FFh)
• Read 16 bits of Manufacture's/Device ID data
• Write 16 bits of data commanding Continuous Conversion Mode (0000h)
• Take CS HIGH.