20
NT538
FUNCTION CODE
The ModBus module supports the following function codes:
3
(10)
: - holding register reading
16
(10)
: - register multiple writing
If ModBus receives a message and a CRC error is detected, 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.
NOTES FOR REMOTE PROGRAMMING
The writable registers are shown in TABLE MODBUS MAPPING referred to as W or RW (write or read / write) max number
of registers 72, see table page. 20.
In the case in which the channel is not enabled and / or the information is not provided we have the following answers:
1. Temperatures measured = 0000 (0 ° C)
2. Temperatures AL. / TRP = value written in E2PROM
3. Channel status = 0000
4. Setting channel =% 00000000, xxxxxxx0% (x = na)
If WRITE data must always respect the rule T_trip> T_alarm and FAN_ON> FAN_OFF.
In case you try to set these thresholds incorrectly, the control unit NT538 will not proceed with the programming and storage
of data, therefore in subsequent readings will read the data from the previous schedule.
After having sent a request for writing the control unit will take a time of about 1 to store the data in eeprom, during the step
of storing the module ModBus will not be able to process additional requests
If the demand for programming is successful, the unit automatically resets and loads the new settings. In the event that
information is sent in writing to a register can’t be written (only READ) data will be trashed without affecting the received
message.
If the information is sent to 4.20mA output = Chan_4 and it is disabled it is forced mode HOT ; the same policy applies to
programming from panel.
The information "RELAY STATUS" indicates the state of excitation of the coils of the relays, so it will be subject to the
commands of "FAILS SAFE".
In the case of writing data "CPU SETTING" with bits "Failsafe Fault" = 0, it will be forced = 1 so as not to affect the validity of
the data packet.
From the point of view of the control unit Modbus connection is considered as a normal NT538.
At the end of the write command (Write) is carried out a check of compatibility data:
• If you have a non-compatibility "exception" for an answer and the data packet is rejected in its entirety. The code
of the first erroneous data can be obtained by reading the log "Error received data" (Note: this code is lost during
RESET or new power or writing data in E2PROM);
• if the data are correct, they are transferred to the non-volatile memory (E2PROM), resets the historical data (Tmax
= 0°C) and is subsequently forced a reset of the system
• If the WRITE command implies only writing "COMANDS" it will be implemented autonomously and without
RESET, ie without affecting the data of the control unit.
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