RTX-24EM
User guide
The technical characteristics can change without notice. AUR°EL S.p.A doesn’t assume the responsibility to the damages caused by an improper use of the device.
AUR°EL S.p.A.
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http://www.aurel.it
9.6
RF operating frequency
The channel register sets the center frequency of the transmission channel used by the EM9209.
The channel is set by the
Frequ[16:0]
register.
Frequency should be between 2400MHz and 2484MHz
Frequ[16..0]
= (32768 x ((Frequency / fref) – 92)) - FreqCorrection
with
Frequency = desired center frequency in MHz.
fref = 26
FreqCorrection = 159
Examples:
Frequency = 2401.5
Frequ[16..0] = 11813 = 0x2E25.
Frequency = 2441.5, Frequ[16..0]= 62226 = 0xF312.
Frequency = 2477.5, Frequ[16..0]= 107597 = 0x1A44D.
FreqCorrection is used to compensate the 26MHz crystal oscillator (internal to the RTX-24EM) deviation.
The channel step is given by 26MHz / 32768 and is approximately equal to 793Hz.
To establish a communication, both linked devices must be set to the same channel. The host
microcontroller can program a channel change, which is validated when SPI signal SS goes down.
Channel spacing of 4 MHz is recommended to limit interference with other RTX-24EM devices operating on
adjacent channels.
9.7
Address byte
For proper communication between two devices, the receiving device must set the
Address[7:0]
register to
match the transmitting device’s
Address[7:0]
register.
The Address byte is used in the packet preamble in order to set the byte start in the bit to byte built-in
reconstruction algorithm.
Decimal value of
Address[7:0]
must be different from
0, 48, 51, 99, 102, 146, 153, 204
. To prevent wrong
packet synchronization when address Rx and Tx differ by a right or left shift, even address values must be
avoided and the most significant bit (MSB) of the first payload byte should be the invert of the address
most-significant bit (MSB).
As the preamble to start packet detection consists of three successive address bytes, the reception can be
triggered by a payload containing such data, even if the transmit and receive addresses are not equal. For
applications where the integrity of the address or the payload is critical, it is recommended to include CRC
or error correction bits inside the payload.
