TMP104 Temperature Chain: 7 Checks for Enumeration and Signed Data
TMP104 Temperature Chain: 7 Checks for Enumeration and Signed Data
TMP104 checks for SMAART Wire wiring, initialization, physical device order, signed temperature bytes and interrupt recovery. This is a documentation-based planning guide, not a report of independent hands-on testing.
1. Identify the interface before connecting a UART
The TMP104 uses the manufacturer SMAART Wire interface with UART-compatible start/stop framing and least-significant-bit-first data. It is not I2C, a generic single-wire protocol or an RS-232 voltage interface. Its supply range is 1.4 V to 3.6 V, so verify host logic levels separately. Document the host transmit and receive connections, sensor supplies and common reference. A familiar UART peripheral can help implement the protocol, but an ordinary terminal session does not perform the required device initialization. Manufacturer documentation.
2. Wire an ordered chain rather than a shared TX bus
Connect the host transmitter to the first RX, then each sensor TX to the next RX, returning the final TX to the host receiver. Do not tie all transmit outputs together as if they were a multidrop open-drain bus. The interface supports up to sixteen devices in the documented chain. Each device normally buffers traffic through but changes that path during enumeration or responses. Inspect continuity, orientation and power at every node before diagnosing missing bytes as a firmware timing problem. Manufacturer documentation.
3. Initialize globally before ordinary register traffic
The calibration byte 0x55 synchronizes communication timing. Global initialization is required before other communications: the documented initialization command is 0x8C, followed by the address-assignment sequence beginning at 0x90. Devices assign and increment addresses as the chain reconnects, and the returned next-address information establishes the detected count. Implement the complete manufacturer sequence rather than transmitting isolated command bytes from this overview. Verify the expected response length and detect an incomplete chain before accepting any temperature values. Manufacturer documentation.
4. Map enumerated IDs to physical thermal locations
An assigned address represents chain order, not a permanent globally unique serial number. Moving, removing or replacing a sensor can shift the relationship between address and physical zone. Preserve a wiring map and check the detected device count after enumeration. For a global read, responses occur in the documented device order and must be associated with the intended register. Do not import a dummy-byte recipe or address convention from a different temperature-sensor family simply because its name or interface appears similar. Manufacturer documentation.
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5. Decode one signed degree per count
Temperature data is signed eight-bit information with 1 degree Celsius per count; 0xFF therefore represents minus 1 degree Celsius. It is not the fractional-degree format used by many other digital thermometers. The temperature register starts at zero until the first conversion, whose typical duration is 26 ms; that typical figure is not a guaranteed universal deadline. Distinguish startup data from a genuine zero-degree environment. Conversion rate, resolution and measurement accuracy are separate specifications and should remain separate in application logs. Manufacturer documentation.
6. Review interrupt clearing and reset side effects
Latched high and low flags depend on the selected latch configuration, and reading configuration clears the latched flags as documented. The global clear-interrupt command 0xA9 also disables future interrupts through the interrupt-enable setting; it is not merely a neutral acknowledgement. Reconfigure monitoring when the application requires it. The global software-reset command retains device IDs, so resetting is not equivalent to a fresh physical-order enumeration. Check the full sequence and returned traffic before assuming every node recovered. Manufacturer documentation.
7. Validate count, freshness and zone meaning together
Record the chain map, detected count, communication timing, selected registers, signed raw bytes and conversion configuration. Exercise host reset, a missing node and a power interruption using a protected low-voltage fixture. A bus timeout or echoed command alone does not prove that all temperature responses arrived. Reject short or misordered records rather than silently shifting zone labels. Only report a zone temperature when device identity, completed conversion and byte decoding are all consistent with the documented chain state. Manufacturer documentation.
Related reading: TMP103 Sensor Network: 7 Checks for Multiple-Device Reads.
Catalog note: The exact-part search did not return a matching Epro listing during preparation. Check the current catalog; this guide makes no price, availability or included-accessory claim.