21
NT210 K
FUNCTION CODE
The ModBus module supports the following function codes:
3
(10)
:
- holding register reading
16
(10)
:
- multiple register writing
If ModBus receives a message and the presence of a CRC error is confirmed, no answer is given.
CODE 3
(10)
.
Request:
Slave address, code 3
(10)
, Starting address HI, Starting address LO, Number of Point HI, Number of Point LO, Crc LO, Crc
HI.
Answer:
Slave address, code 3
(10)
, Byte count, Data HI, Data LO……., Crc LO, Crc HI.
CODE 16
(10)
.
Request:
Slave address, code 16
(10)
, Starting address HI, Starting address LO, Number of Point HI, Number of Point LO, Byte count,
Data HI, Data LO……., Crc LO, Crc HI.
Answer:
Slave address, code 16
(10)
, Starting address HI, Starting address LO, Number of Register HI, Number of register LO, Crc
LO, Crc HI.
The writable registers contain the following data: Alarm, Trip, Fan-on, Fan-off.
So the possible starting addresses are:
00-17
for alarm and fan,
00-25
for the Trip thresholds. The Number of Point LO
parameter can be set only to 8.
If a writing request is sent to an address other than the above, ModBus shall answer with an error code 02 (incorrect data
address).
If a writing request is sent for more than 8 registers (Number of point LO), ModBus will not be able to accept the
request and will not answer, so the request will time out.
NOTES FOR REMOTE PROGRAMMING
If an NT210 K needs to be programmed, it is necessary to remember that the Temperature, Pressure and Level alarm
settings must be modified selecting 8 registers at a time (registers 00-17, 00-18 ......... 00-24).
The same must be remembered for the Trip thresholds (registers 00-25, 00-26 ......... 00-32) and for each quantity measured
(Temperature, Pressure, Level).
Note: the Alarm level thresholds must be programmed in the register number 20 selecting 2 for active the function. The Trip
level thresholds must be programmed in the register number 28 selecting 1 for active the function.
Also in the remote programming stage via ModBus it is necessary to consider that the Alarm thresholds must be lower than
the Trip thresholds and that the Fan-on thresholds must be higher than the Fan-off thresholds.
If an attempt is made to set these thresholds incorrectly, the NT210 K control unit will not set and store the data, so the data
of the previous programming will not be changed.
Before restarting ERR is displayed.
After sending a writing request the control unit will take about 1" to store the data in eeprom; while storing the ModBus
module will not be able to process any other requests.
If the programming request is successful, the control unit resets automatically and loads the new values. Before restarting
PRG is displayed.
ERROR CODES (exception code)
If the request is incorrect, ModBus will answer with modified codes and codified errors as follows:
1.
Unsupported function code
2.
Incorrect data address
3.
Incorrect data (i.e. length)
POLLING FREQUENCY
The maximum time to answer a call never exceeds a second, so we recommend shorter polling frequencies are not
adopted. In multi-device RS485 lines, interrogated in sequence, it may be useful to enter a delay between polls in relation
to: the number of connected devices, the communication speed, and the number of readings registers.
