20
NT935-4
ASERIES
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 writeable registers are shown in the MODBUS MAPPING TABLE as W or RW (
write or read/write)
max number of
registers 72, see table page. 22.
If a channel is not enabled and/or the information is not provided for, the following answers are given:
1.
Measured temperatures
= 0000 (0°C)
2.
Temperature AL./TRIP
= Value written in E2PROM
3.
Channel state
= 0000
4.
Channel setting
= %00000000; %xxxxxxx0 (x=n.d.)
Also in remote programming via ModBus you must take into consideration 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 you try to set these thresholds wrongly, the NT935 AD
monitoring unit won’t proceed with programming and data storage;
therefore in the following readings you will read the data relevant to the previous programming.
After sending a writing request, the monitoring unit will require approximately 1’’ to store the data in eeprom; during the
storage phase, the ModBus module will not be able to process other requests.
If the programming request is successful, the control unit automatically resets and loads the newly set values.
If the information is sent to 4.20mA channel CHn and it is disabled it is forced mode " HOT" ; the same policy applies to
programming from panel.
The "RELAYS STATUS" information indicates the state of excitation of the coils of the relays, so it will be subject to the
"FAIL SAFE" commands.
If writing information is sent towards a READ-only register, the data will be binned without affecting the message received.
At the end of the Write command, data compatibility is checked:
1.
In case of incompatibility, the answer is an "exception" and the data packet is refused in full. The code of the
first wrong datum can be requested reading the "Datum error received" register. (NB: this code is lost during
RESET, switching on or data writing in E2PROM);
2.
If the data are correct, they are transferred into the non-volatile memory (E2PROM), historical data are
cancelled (Tmax=0°C) and, then, a system RESET is forced.
3.
If the WRITE command entails only writing "COMMANDS", it will be performed autonomously and without a
RESET, that is without affecting the control unit data.
