Specifications

OPERATIONS
Page 100 MRC-565 Packet Data Radio Operations & Maintenance
Continuous Measurements aR0! ... aR9! a<values><CR><LF> (formatted like the D commands)
Continuous Measurements + CRC aRC0! ... aRC9! a<values><CRC><CR><LF> (formatted like the D
commands)
*These commands may result in a service request.
5.9.10 Serial Port Command and Response Diagrams
Figure 11. Data Port Byte Stream Timing and Data Byte Format
The Diagrams above summarize the type of command/response that is used in the SDI-12
protocol. The data rate is always 1200 baud. The BREAK signal is a minimum of 12ms at +5V
followed by at least 8.33ms of a MARK signal at 0V. The purpose of the BREAK is to wake up
all the sensors on the line.
The “line” is a single wire in tri-state mode where the Recorder is master and the Sensors are
slaves. Only one device can transmit at a time, the master device always initiates
communication, and the slaves always respond to commands addresses to them, are received
correctly, and are valid in format and content.
The first byte of each command and response is a 1-byte sensor address. Valid addresses are 0-9,
A-Z and a-z. The last byte of a command is always a ‘!’ character. Response strings always
begin with the sensor address and end with <cr><lf>.
Each byte has 1 start bit, 7 data bits, 1 parity bit and 1 stop bit. The start bit is +5V. The data and
parity bits are Negative polarity where a ‘0’ is +5V and a ‘1’ is 0V. The stop bit is 0V. The bytes
that a device sends should have no space between them, but the protocol allows up to 1.66ms
between bytes.
low power
command
wake-up command acknowledge
send data command data report with one value
break
a
mark
M
! \r \n a
D 0
!
a
a
+
1
2 3
4
0
5
.
6 7
\r
\n
0
0
1
12ms
8.33
ms
wake
up
delay
15-100ms
always has +/- sign but may not
have the decimal point if it is an
integer value. So it can be from
2 to 9 bytes including sign and
decimal point.
MASTER
SLAVE
varies from 1 to 7 digits
S
1 2
3
4 5 6 7
S
P
time
data bits
even
parity
bit
Start
bit (high)
Stop
bit(low)
Least significant bit
is sent first
Data Port Byte Stream Timing Diagram
Data Byte Format
+5V = 0
0V = 1