Appendix B __________________________________________________________ SDI-12 Protocol
VAISALA______________________________________________________________________ 197
-
A data recorder transmits a break by setting the data line to spacing
for at least 12 ms.
-
The sensor does recognize a break condition for a continuous
spacing time of less than 6.5 ms. The sensor will always recognize
a break when the line is continuously spacing for more than 12 ms.
-
When receiving a break, a sensor must detect 8.33 ms of marking
on the data line before it looks for an address.
-
A sensor must wake up from a low-power standby mode and be
capable of detecting a start bit from a valid command within
100 ms after detecting a break.
-
After a data recorder transmits the last character of a command, it
must relinquish control of the data line within 7.5 ms.
0505-218
Figure 46
Timing Diagram
-
After receiving the break and the command, the addressed sensor
sets the data line to marking at 8.33 ms and then sends the response
(tolerance: -0.40 ms). The start bit of the first response byte must
start within 15 ms after the stop bit of the last byte of the command
(tolerance: +0.40 ms).
-
After a sensor transmits the last character of a response, it must
relinquish control of the data line within 7.5 ms (tolerance:
+0.40 ms).
-
No more than 1.66 ms of marking are allowed between the end of
the stop bit and the start bit (for example between characters) on
any characters in the command or the response (no tolerance.) This
