A controller transmitted a 20-byte Zigbee API frame, but LabVIEW displayed different values and appeared to group the received data into four-digit hexadecimal words. The display grouping was not evidence that LabVIEW converted 8-bit bytes into 16-bit integers. The confirmed fault ultimately resided on the Zigbee side of the device.
Compare the Transmitted and Received Data
| Observation | Evidence | Engineering conclusion |
|---|---|---|
| Confirmed transmission | 7E 00 10 10 01 00 13 A2 00 40 3C 87 B4 C8 FD 00 00 68 69 EC |
The transmitted frame contains 20 bytes. |
| LabVIEW display | 7E00 0E90 0013 A200 403C 87B5 0000 0168 6930 |
Four-digit groups can be a display-format choice; grouping alone does not prove 16-bit conversion. |
| Read length set to 18 bytes | The response appeared after one transmission. | The configured read count changes when the application returns data. |
| Read length set to 20 bytes | The returned data ended with 7E00, matching the start of the next frame. |
The read crossed a frame boundary or waited for additional data. |
Separate Hex Formatting from Data Corruption
A hexadecimal indicator can present consecutive bytes as four-digit groups without changing the underlying byte stream. Therefore, changing the display to two hexadecimal digits per byte may improve inspection, but it cannot correct altered values such as B4 appearing as B5 or missing frame content.
Validate the raw byte sequence independently of its visual grouping. Compare byte positions and total byte count against the confirmed 20-byte transmission instead of interpreting each four-digit display group as a received 16-bit value.
Check Framing and Read Boundaries
- Match the serial configuration at both endpoints, including baud rate, parity, data bits, and start and stop bits. An outside terminal receiving plausible data is useful evidence, but it does not replace checking the settings used by the LabVIEW session.
- Inspect the actual read buffer and its returned byte count. A request for 20 bytes can wait for 20 bytes or terminate on a timeout; requesting 18 bytes cannot capture the complete confirmed 20-byte frame.
- Look for the next frame delimiter in the result. A trailing
7E00that repeats the beginning of the message shows that the read consumed bytes from a subsequent transmission. - Capture the same transmission at the Zigbee interface and at the LabVIEW input. If the bytes differ before LabVIEW formats them, investigate the Zigbee device or interface rather than the hexadecimal display.
Confirmed Root Cause and Verification
The final diagnosis placed the fault on the Zigbee side of the device, not in LabVIEW's selection of an 8-bit or 16-bit hexadecimal display. After correcting that side, verify that one transmission yields all 20 expected bytes in order and that the read neither truncates the frame nor appends the opening bytes of the next frame.
FAQ
Why does LabVIEW show serial bytes as four-digit hex values?
The hexadecimal display can group consecutive bytes into four-digit fields. That presentation does not by itself mean LabVIEW converted the received byte stream into 16-bit integers.
Why does a LabVIEW serial read end with the start of the next Zigbee frame?
If the requested byte count is not satisfied by the current data, the read can include bytes from a later transmission. In this case, trailing 7E00 repeated the beginning of the next frame.
What caused the incorrect Zigbee serial bytes in this case?
The fault was confirmed on the Zigbee side of the device. Serial framing and LabVIEW read-length checks were still useful for separating transport, buffering, and display-format issues.