IE-SNC-T33(4)19+T73(4)11-09
7
Setting of pressure correction for altitude
For devices T7311 and T7411 only! If there is necessary to read value of atmospheric
pressure corrected with respect to altitude, it is possible to set corresponding pressure offset for this
altitude. It is possible to do it with Users software. This value is then automatically added to
measured pressure value. The resultant value of pressure with added correction for altitude must be
between 300 hPa and 1350 hPa (from 4.351 PSI to 19.580 PSI). Outside this range device sends
value of Error 2!
Description of communication protocols
Detailed description of each communication protocols including examples of
communication is available in individual document “
Description of communication protocols of
Txxxx series”
which is free to download at
www.cometsystem.cz
.
Note: After switching ON the power of the device it can last up to 2 s before the device starts to
communicate and measure!
Modbus RTU
Control units communicate on master-slave principle in half-duplex operation. Only master
can send request and only addressed device responds. During sending of request no other slave
station should respond. During communication, data transfer proceeds in binary format. Each Byte
is sent as eight bit data word in format: 1 start bit, data word 8 bit (LSB first), 2 stop bits
1
, without
parity. Device supports communication speed from 110Bd to 115200Bd.
Sent request and response have syntax: ADDRESS OF DEVICE – FUNCTION – Modbus CRC
Supported functions
03 (0x03)
: Reading of 16-bit registers (Read Holding Registers)
04 (0x04)
: Reading of 16-bit input gates (Read Input Registers)
16 (0x10)
: Setting of more 16-bit registers (Write Multiple Registers)
Jumper and button
Jumper and button are located next to connection terminals. If communication protocol
Modbus is selected the function of jumper and button is as follows:
•
Jumper opened – device memory is protected from writing, from the device side it is only
enabled to read measured value, writing to memory is disabled (no change of device
address, communication speed and LCD setting is enabled).
•
Jumper closed – writing to device memory is enabled by means of User’s software.
•
Jumper opened and button shortly pressed – device goes to Info mode, see chapter „
Info
mode
“.
•
Jumper closed and button pressed for longer than six seconds – causes restoring of
manufacturer setting
of communication protocol
, i.e. sets Modbus RTU communication
protocol, device address sets to 01h and communication speed to 9600Bd - after button press
there is “dEF” message blinking at LCD display. Six seconds later message “dEF” stays
shown, it means manufacturer setting
of communication protocol
is done.
1
Device sends two stop bits, for receive one stop bit is enough.
