Campbell Scientific Sentek EnviroSCAN EasyAG SDI-12 Manual v 3.4 - Manual (Page 12)

EnviroSMART & EasyAG SDI-12 Probe Manual
Copyright © 1991 – 2003 Sentek Pty Ltd All rights reserved Page 7
In this example shown in Figure 3, there is no inter-character gap sent by the SDI-12 probe interface.
The start bit for the second character follows immediately after the stop bit (marking) from the first
character.
Note: The EnviroSMART and EasyAG SDI-12 probe interface will permit up to 4 bit-times between
characters before rejecting the command.
Marking 8.4 mS
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
Intervals approx 0.8mS (1 bit time)
?=3F !=21
1 1 1 1 1 1 0 0 1 0 0 0 0 1 0 0
Break -
Min 12 mS
Marking Level
Spacing Level
Figure 3: Voltage levels on the SDI-12 line during an Acknowledge Active command (a!)
Following the terminating character (!) of the command, the controlling device must release the line
within 6.5mS. The EnviroSMART and EasyAG SDI-12 probe interface will hold the line at the
marking level for a minimum of 8.33mS before transmitting the first character of the response.
Addresses
The EnviroSMART and EasyAG SDI-12 probe interface accepts SDI-12 addresses in the range “0”
to “9”, “A” to “Z” and “a” to “z”. Setting the probe interface address can be done using the Change
Address command (aAb!) (see SDI-12 Commands Supported) or using the Intelligent Probe
Configuration Utility.
Note: If the new address is invalid, the current address will be kept.
Note: The probe interface will remain unresponsive for approximately 30 ms while the new address is
saved in non-volatile memory.
Note: The probe interface supports “?” (wildcard) as an address only for the Acknowledge Active
command (a!).
3.5V
1.0V
Bit Number:
Bit Value: