Hanna Instruments HI 21 Series - Manual (Page 16)

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Command Parameter Description
CAR null Request calibration data
GET NN Request setup item NN
K 01 null Same as CFM+ +CAL keys
K 02 null Same as LCD+CAL+SETUP keys
KCD null Same as CAL DATA key
KCF null Same as CFM key
KCL null Same as CAL key
KDS null Same as LCD key
KDW null Same as key
KRG null Same as key
KST null Same as SETUP key
KUP null Same as key
MDR null Request firmware code
MVR null Request mV reading
(HI 22 only; available in
control or idle mode only)
PHR null Request pH reading
(HI 21 only; available in
control or idle mode only)
PWD NNNN Send the 4-digit password
SET NNPC
1
C
2
C
3
C
4
C
5
Set setup item NN to the
PC
1
C
2
C
3
C
4
C
5
value
P=+ if value is greater than 0
P=- if value is less than 0
C
1
can be 0 or 1 only
C
2
C
3
C
4
C
5
can be 0 to 9 or
blank (the command is
not available if the controller is
in setup mode)
TMR null Request temperature reading
As additional feature, the controller is also
provided with two pins (5V and 0V) in or-
der to apply the Fail Safe Open Line
protection method. To avoid erroneous
readings in Open-Line conditions, pull-
up and pull-down resistors should be
connected as shown.
The Fail-Safe resistors are connected only to one unit in the
line, and their value depends on the application and char-
acteristic impedance of the connection cable.
The RS485 port is optoisolated from measuring circuit and
power line. If both analog output and RS485 port are present,
they have the same ground.
RS485 PROTOCOL
The commands sent to the controller must have the following
format:
• 2-digit process ID number
• 3-character command name
• Parameters (variable length, may be null)
• End of command (always the CR character, Hex 0D)
A maximum time interval of 20 ms is allowed between two
consecutive characters of a command.
It is possible to send commands to change the controller
settings or to simply ask information on the controller status.
Following is the complete list of commands available: