PIC12LF1840T48A-I Datasheet, PDF (1/10 Pages) Microchip Technology – Using the PIC12LF1840T48A Microcontroller with Integrated Sub-GHz Transmitter

AN1393
Using the PIC12LF1840T48A Microcontroller with
Integrated Sub-GHz Transmitter
Author: Cristian Toma
Microchip Technology Inc.
INTRODUCTION
The PIC12LF1840T48A is a Microchip microcontroller
that has an on-board transmitter. The transmitter is
suitable for operation in the 418, 434 and 868 MHz
license-free ISM bands. The modulation is On/Off
Keying (OOK) or Frequency-Shift Keying (FSK). This
document describes the complete implementation of a
radio transmitter using the PIC12LF1840T48A.
KEY REQUIREMENTS
The RF transmitter integrated into the
PIC12LF1840T48A has two main functioning modes.
One operation mode, called Preset mode, allows the
user to choose from two predefined modes of
operation. The setting is done by either pulling the
CTRL line low or high. One connection to the DATA line
is required to send modulation data to the transmitter.
TABLE 1: AVAILABLE PREDEFINED
CONFIGURATIONS
CTRL = 1
433 MHz
OOK modulation
10 dB output power
CTRL = 0
868.3 MHz
FSK modulation
Fdev = 20 kHz
10 dB output power
If one of the pre-defined configurations (see Figure 1)
is used, then there is no need to use an extra I/O pin to
control the CTRL line of the transmitter. This pin must
be either pulled high (using a resistor > 20 KOhm, but
less than 1 MOhm), or pulled low.
Another operation mode is called Advanced mode.
This mode is useful when the user needs a custom
configuration that cannot be satisfied using one the two
preset modes. This custom configuration can include
custom settings, such as different transmitting
frequency, RF output power, transmit power-off timer,
fine tuning of the transmitting center frequency,
different modulation format, and frequency deviation (if
FSK mode is used).
If the Advanced mode is used, the user must
implement the two-wire interface required to write data
to the Configuration register. Please refer to Table 1 for
the full description of the Configuration register.
In this case, an extra I/O pin is needed to control the
CTRL pin, acting as a clock line. The DATA line of the
transmitter must be connected to an I/O pin of the
microcontroller section. This is used to carry both data
transmitter over-the-air, and Configuration data (when
used in conjunction with the CTRL line). The current
reference design has the DATA line connected to the
CCP1 line of the microcontroller. This is because the
KEELOQ® security IC encoder implementation takes
advantage of the internal ECCP peripheral to send
KEELOQ security IC data packets.
CONFIGURATION REGISTER WRITE
The transmitter can be software-configured to use
different transmitting frequencies, different modulation
and different frequency deviations (in FSK mode). All
these settings are done by using a serial interface
(using the CTRL line as clock line, and DATA as data
line). A total of 16 are clocked, consisting of a Start bit
(logic zero), a read/write bit, and the 12-bit
Configuration register (see Figure 1).
CONFIGURATION REGISTER READ
It is also possible to read back the information stored
into the Configuration register. Reading operation is
done in a similar way to writing data. The read/write bit
is logic ‘1’ in this case. Please note that, when reading
back data from the Configuration register, a total of 64
clock cycles are required (see Figure 2). Reading only
the 13-bit Configuration bits is not allowed. Please
notice that the DATA line from the transmitter section
becomes an output pin after the 8^th falling edge of the
CTRL line. Care must be taken to change the
microcontroller port connected to the DATA line from
output to input. After reading all the data, the port must
be put back into Output mode. Reading back
information from the Configuration register is not
required. This can be helpful during the software
development phase. This feature is not used in normal
operation mode.
 2011 Microchip Technology Inc.
DS01393B-page 1