XE8806A SEMTECH [Semtech Corporation], XE8806A Datasheet - Page 99

• Manufacturer Part Number: XE8806A
• Description: Ultra Low-Power Low-Voltage
• Manufacturer: SEMTECH [Semtech Corporation]

14.12.1.4.3
To handle the transmission data by interrupt, enable the RF interface transmission interrupt in the interrupt handler
of the circuit.
We need to send the start sequence (preamble) first. The start sequence is defined as 4 bytes of “01010101”.
Since the NRZ Space encoder is enabled, four bytes of “00000000” should be written to the register RegRfifTx.
After encoding, this will correspond to 4 bytes of “01010101”. The FIFO is now full, and we can wait for the
interrupt, which will indicate that the FIFO is empty.
At occurrence of the interrupt, 4 bytes of the message can be written to the FIFO until all message bytes are sent.
14.12.1.5 Transmission mode using Miller code
The messages have to be encoded using the Miller code. The start sequence of the message is a protocol
violation. The messages are sent at a data rate of 5 kbit/s (or 10 kbaud/s in Miller code) and the modulator
frequency deviation is 25kHz and the output power is +5dbm.
the transmission data.
14.12.1.5.1
To set the XE1201A in transmission mode, set the pin EN to 1 and the pin RXTX to 0. The modulator deviation
frequency is set to 23.4kHz by writing C(6:0) = 0000110. The output power is set to +5dbm by writing C(13:12) =
11. All other values remain default. The resulting register values are shown in Table 14-25.
14.12.1.5.2
Set-up the RF interface of the microcontroller circuit as a transmitter (RfifEnRx = 0 and RfifEnTx = 1).
Assume that the RC clock frequency used in the microcontroller is 2.0 MHz. To select the correct baud rate of 5
kbit/s according to the equation in chapter 14.10 (attention: the baud rate is twice the bit rate in the Miller code),
fine*coarse=2.0e06/(16*10e3)=12.5. We can approximate this at 12, which gives us a data rate of 5.2 kbit/s. This
can be done by setting RfifBRCoarse = 01 and RfifBRFine = 0010. If a data rate closer to the 5kbit/s target, the
RC oscillator frequency could be slightly increased to 1.04 MHz which gives fine*coarse=13.
The external bit synchronization clock is switched off by clearing the bit RfifTxClock = 0.
The encoder is enabled and set to Miller encoding by setting RfifEnCod = 1 and RfifPCM = 111.
The set-up of the interface is summarized in Table 14-26.
© Semtech 2006
The following paragraphs will show how to set-up the XE1201A, how to set-up the RF interface and how to handle
Register
Register A
Register B
Register C
Table 14-25. XE1201A register set-up (see XE1201A datasheet for bit explanation)
Data transmission
XE1201A set-up
RF interface set-up
0
0
1
13
0
0
1
12
RegRfifCmd1
RegRfifCmd2
RegRfifCmd3
Register
Table 14-26. RF interface set-up
0
0
0
11
0
0
1
10
0
0
0
9
14-19
0
0
1
8
0
0
0
7
0
0
0
6
00010010
00100111
00000001
contents
0
0
0
5
1
0
0
4
0
0
0
3
XE8806A/XE8807A
0
0
1
2
0
0
1
1
0
0
0
0
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