User Manual
RM169-1
Pag. 31
Doc. MI004760-E
Rev. 0
www.seneca.it
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BE REPRODUCED WITHOUT PRIOR PERMISSION.
communications test the diagnostic parameters are also sent. These are: Local RSSI, Remote RSSI, Remote
VBatt. These values enable the assessment of the intensity of the radio signal received both from the remote
and local units. The RSSI fields are expressed in dBm and have a resolution of 0,0625 dbm. In another box the
value of the supply voltage of the remote radiomodem is displayed.
The RSSI provides a correct measurement in the range from -100 to -50 dBm. Values less than -100 dBm (for
example -105, -110 dBm) may create communication problems. The saturation of the measured RSSI restricts
the maximum value indicated approximately to -47 dBm ± 3dBm, signals of greater intensity return the same
indication.
Note
: If, in the radio link, one or more digipeater units are used, the level of the RSSI is always referred to the
last received signal of the radio stations chain. Example: with four units present in the network (Master "A", first
digipeater "B" , second digipeater "C", slave "D") the RSSI read from the slave "D" is referred to the reception of
the digipeater "C", while the RSSI read from the master A is referred to the reception of the digipeater "B".
If you wish to use the readings of diagnostic (RSSI and VBatt) outside the configurator, the communication with
the radiomodem must use the serial data format "9600,N,8,1". The radiomodem send the following hex string:
System code
(one byte),
Flag options
(one byte, value 0x08),
quantity of addresses
(one byte),
digipeater
addresses
(from 0 to 8 bytes),
target address
(one byte), one
character
(one byte).
Example: 0x01, 0x08, 0x01, 0x01, 0x55. This example uses the system code 1 with only one address: the target
(1). The last character (here 0x55) can be of any other value.
The radio modem returns a string consisting of
six bytes
:
Remote RSSI
(two bytes),
VBatt remote
(two bytes),
local RSSI
(two bytes). For each pair, the first byte received is always the least significant byte.
The value of the RSSI is in the format 16-bit signed integer and has a resolution of 0.0625 dbm. Divide the RSSI
value by 16 to obtain the result with a step of 1 dbm.
The value of the battery voltage is in the format 16-bit unsigned integer. The formula used to derive the supply
voltage in volts is the following: read value * 0.0048828125.
The diagnostic request (bit 3 of the byte flag = set) excludes the normal data exchange.
