Vaisala WXT510 - Manual (Page 143)

Appendix B __________________________________________________________ SDI-12 Protocol
VAISALA ______________________________________________________________________ 141
- When receiving a break, a sensor must detect 8.33 milliseconds 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
milliseconds 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 milliseconds.
0505-218 Figure 24 Timing Diagram
- After receiving the break and the command, the addressed sensor
sets the data line to marking at 8.33 milliseconds and then sends the
response (tolerance: -0.40 milliseconds.) The start bit of the first
response byte must start within 15 milliseconds after the stop bit of
the last byte of the command (tolerance: +0.40 milliseconds).
- After a sensor transmits the last character of a response, it must
relinquish control of the data line within 7.5 milliseconds
(tolerance: +0.40 milliseconds.)
- No more than 1.66 milliseconds 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 permits a response to an M command to be sent
within a 380-millisecond window.
- Sensors must return to a low-power standby mode after receiving
an invalid address or after detecting a marking state on the data line
for 100 milliseconds (tolerance: +0.40 milliseconds).
- When a recorder addresses a different sensor, or if the data line has
been in the marking state for more than 87 milliseconds, the next
command must be preceded by a break.