Timing – Campbell Scientific Sentek EnviroSCAN EasyAG SDI-12 Manual v 3.4 User Manual

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EnviroSMART & EasyAG SDI-12 Probe Manual

Page 6

Figure 2: EnviroSMART® and EasyAG® SDI-12 probe interface communication power sequence

Timing

Figure 3 shows voltage levels on the SDI-12 line during transmission of an Acknowledge Active

command (a!) using the “?” (wildcard) address.

After the break condition has been sent to the EnviroSMART or EasyAG SDI-12 probe interface by

holding the line high (above 3.5V, spacing) for 12mS, the line is held low (below 1 V, marking) for a

minimum of 8.3mS before the first character is transmitted.

Each character transmitted consists of a Start Bit (spacing), followed by 7 data bits, followed by an even

parity bit, followed by a stop bit (marking). Characters are transmitted least significant bit (LSB) first

with each bit in the character being 0.833mS wide.

EnviroSMART or

EasyAG SDI-12 probe

interface in sleep mode

15 second timeout

process command

(including response)

break

yes

sample sensors

sleep mode

standby mode

sampling mode

250

100

(Moisture)

130mA

(Salinity)

valid

communication

received?