? 2011 microchip technology inc. ds01393b-page 1 an1393 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. 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 tab l e 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 k ee l oq ? security ic encoder implementation takes advantage of the internal eccp peripheral to send k ee l oq 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. 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 author: cristian toma microchip technology inc. using the pic12lf1840t48a microcontroller with integrated sub-ghz transmitter
an1393 ds01393b-page 2 ? 2011 microchip technology inc. table 2: config uration register bit name state setting default notes ctrl = 0 ctrl = 1 d12 tx mode 0 automatic wake-up 0 0 when set to ? 1 ?, the transmitter will continuously transmit. when set to ? 0 ?, the transmitter will go to sleep mode after a 2 ms inactivity on the data line. 1 forced transmit d(11:9) frequency 000 418.00 mhz 100 010 rf operating center frequency. 001 433.42 mhz 010 433.92 mhz 011 864.00 mhz 100 868.30 mhz 101 868.65 mhz 110 868.95 mhz 111 869.85 mhz d8 modulation 0 fsk 0 1 modulation format. 1 ook d(7:5) freq. deviation 000 10 khz 010 010 fsk frequency deviation (not used in ook mode). 001 12.5 khz 010 20 khz 011 25 khz 100 40 khz 101 50 khz 110 80 khz 111 100 khz d4 rf power 0 0 dbm 1 1 programmed rf output power. 1 1 dbm d3 tx timer 0 2 ms 0 1 transmit power-off timer. 1 20 ms d(2:0) fine tuning 011 fc + 6 * pll step 000 000 fine tuning from programmed center frequency. 010 fc + 4 * pll step 001 fc + 2 * pll step 000 fc + 0 * pll step 111 fc - 2 * pll step 110 fc - 4 * pll step 101 fc - 6 * pll step 100 fc - 8 * pll step
? 2011 microchip technology inc. ds01393b-page 3 an1393 figure 1: configuratio n register write figure 2: configurat ion register read powering-on the transmitter when the transmitter is not active (no rf emission), the entire transmitter section is in sleep mode. when using the advanced mode, the transmitter can be placed in transmit mode in two ways. this is dependent of the bit d12 in the configuration word (tx mode). 1. when tx mode = 0 : a rising edge on the data line activates the start-up process. the data pin must be held high for a period longer than the transmitter start-up time (2 ms). after this start-up pulse, the transmitter is ready to send data over-the-air. the transition back to sleep mode is done automatically after an inactivity period, in which the data line is held low. this power-off time is programmable using the d3 bit in the configuration register. the available settings are 2 ms and 20 ms. if the transmitter implements k ee l oq ? , we recommend using a power-off time of 20 ms. this is because a typical k ee l oq pocket includes a 2 ms header, which could be interpreted by the transmitter as a time-out period and the transmitter will shut down. 2. when tx mode = 1 : when setting the d12 bit to logic 1 (by writing to the configuration register), the transmitter will be placed directly into transmit mode. after setting the bit, a transmitter start-up time (2 ms) is required. after this start-up period the transmitter is ready to send data over-the-air. the transmitter will remain in transmit mode until bit d12 is set back in logic zero. the above (when d12 = 0 ) power- off time is applied (2 or 20 ms). when using the preset mode, only the automatic start- up mode is available. the data pin must be held high for a period longer than the transmitter start-up time (2 ms). after this start-up pulse, the transmitter is ready to send data over-the-air. the transition back to sleep mode is done automatically after a period of 2 ms (when using the preset mode for 433 mhz ook), or 20 ms (when using the preset mode for 868 mhz fsk). ctrl data r/w d11 d8 d5 d2 acc d12 d10 d9 d7 d6 d4 d3 d1 d0 ?0? ?0? ?0? ctrl data r/w ?0? ?0? d10 d0 acc ?0? ?0? ?0? d12 d11 d1 t42 t41 ?0? ?1? ?0? t1 t0 legend: data pin is an output.
an1393 ds01393b-page 4 ? 2011 microchip technology inc. transmitter configuration the transmitter can be configured by writing to the configuration register. the following codes show a transmitter configuration example. the following definitions ( example 1 ) can be found in the 12lf1840t48asettings.h file: example 1: the following functions ( example 2 ) can be found in the 12lf1840t48acommands.c file: example 2: configuring the transmitter is done by calling the sendtxcommand function. this command takes as parameter a bitwise or with the selected configuration ( example 3 ). example 3: figure 3: antenna design. overall board dimensions #define t48_auto_wake_up 0b0000000000000 #define t48_forced_tx 0b1000000000000 #define t48_freq_41800 0b0000000000000 #define t48_freq_43342 0b0001000000000 #define t48_freq_43392 0b0010000000000 #define t48_freq_86400 0b0011000000000 #define t48_freq_86830 0b0100000000000 #define t48_freq_86865 0b0101000000000 #define t48_freq_86895 0b0110000000000 #define t48_freq_86985 0b0111000000000 #define t48_mod_fsk 0b0000000000000 #define t48_mod_ook 0b0000100000000 #define t48_dev_10k 0b0000000000000 #define t48_dev_12k 0b0000000100000 #define t48_dev_20k 0b0000001000000 #define t48_dev_25k 0b0000001100000 #define t48_dev_40k 0b0000010000000 #define t48_dev_50k 0b0000010100000 #define t48_dev_80k 0b0000011000000 #define t48_dev_100k 0b0000011100000 #define t48_tx_0db 0b0000000000000 #define t48_tx_10db 0b0000000010000 #define t48_tx_2ms 0b0000000000000 #define t48_tx_20ms 0b0000000001000 #define t48_tune_6pll 0b0000000000011 #define t48_tune_4pll 0b0000000000010 #define t48_tune_2pll 0b0000000000001 #define t48_tune_0pll 0b0000000000000 #define t48_tune_-2pll 0b0000000000111 #define t48_tune__4pll 0b0000000000110 #define t48_tune__6pll 0b0000000000101 #define t48_tune__8pll 0b0000000000100 void sendtxcommand (int cmd) { sendbytetxcommand((cmd & 0xff00) >> 8); sendbytetxcommand((cmd & 0x00ff)); } void sendbytetxcommand(unsigned char cmd) { char i; for (i=0; i<8; i++) { if (cmd & 0x80) ra2 = 1; else ra2 = 0; ctrl = 1; nop(); nop(); ctrl = 0; cmd = cmd << 1; } } sendtxcommand ( t48_auto_wake_up | t48_freq_43392 | t48_mod_ook | t48_dev_20k | t48_tx_10db | t48_tx_20ms| t48_tune_0pll );
? 2011 microchip technology inc. ds01393b-page 5 an1393 figure 4: antenna design. loop antenna dimensions conclusion the pic12lf1840t48a is a microchip microcontroller with an integrated rf transmitter. this document helps the user design a transmitter using this device. a high level of integration combined with a large variety of rf configurations and an overall low cost make this design an ideal solution for a radio transmitter. this device is fully compatible with the existing k ee l oq security solutions.
an1393 ds01393b-page 6 ? 2011 microchip technology inc. appendix a: revision history revision a (9/2011) initial release. revision b (11/2011) revised title; revised figure 5.
? 2011 microchip technology inc. ds01393b-page 7 an1393 annex ? transmitter schematics a reference schematic diagram with an rf filter and matching network is provided. the component values are given for 433.92 mhz. the crystal is a low-cost 26 mhz hc-49. figure 5: reference desi gn transmitter schematic ? using the ctrl line + - pickit? 2 3v coin cell v dd v ss v dd v dd v pp
an1393 ds01393b-page 8 ? 2011 microchip technology inc. figure 6: reference desi gn transmitter schematic ? using the preset mode 3v coin cell pickit? 2 v dd v dd v dd v dd v dd v dd
? 2011 microchip technology inc. ds01393b-page 9 information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. it is your responsibility to ensure that your application meets with your specifications. microchip makes no representations or warranties of any kind whether express or implied, written or oral, statutory or otherwise, related to the information, including but not limited to its condition, quality, performance, merchantability or fitness for purpose . microchip disclaims all liability arising from this information and its use. use of microchip devices in life support and/or safety applications is entirely at the buyer?s risk, and the buyer agrees to defend, indemnify and hold harmless microchip from any and all damages, claims, suits, or expenses resulting from such use. no licenses are conveyed, implicitly or otherwise, under any microchip intellectual property rights. trademarks the microchip name and logo, the microchip logo, dspic, k ee l oq , k ee l oq logo, mplab, pic, picmicro, picstart, pic 32 logo, rfpic and uni/o are registered trademarks of microchip technology incorporated in the u.s.a. and other countries. filterlab, hampshire, hi-tech c, linear active thermistor, mxdev, mxlab, seeval and the embedded control solutions company are registered trademarks of microchip technology incorporated in the u.s.a. analog-for-the-digital age, app lication maestro, chipkit, chipkit logo, codeguard, dspicdem, dspicdem.net, dspicworks, dsspeak, ecan, economonitor, fansense, hi-tide, in-circuit serial programming, icsp, mindi, miwi, mpasm, mplab certified logo, mplib, mplink, mtouch, omniscient code generation, picc, picc-18, picdem, picdem.net, pickit, pictail, real ice, rflab, select mode, total endurance, tsharc, uniwindriver, wiperlock and zena are trademarks of microchip technology incorporated in the u.s.a. and other countries. sqtp is a service mark of microchip technology incorporated in the u.s.a. all other trademarks mentioned herein are property of their respective companies. ? 2011, microchip technology incorporated, printed in the u.s.a., all rights reserved. printed on recycled paper. isbn: 978-1-61341-842-0 note the following details of the code protection feature on microchip devices: ? microchip products meet the specification cont ained in their particular microchip data sheet. ? microchip believes that its family of products is one of the mo st secure families of its kind on the market today, when used i n the intended manner and under normal conditions. ? there are dishonest and possibly illegal methods used to breach the code protection feature. all of these methods, to our knowledge, require using the microchip produc ts in a manner outside the operating specifications contained in microchip?s data sheets. most likely, the person doing so is engaged in theft of intellectual property. ? microchip is willing to work with the customer who is concerned about the integrity of their code. ? neither microchip nor any other semiconductor manufacturer c an guarantee the security of their code. code protection does not mean that we are guaranteeing the product as ?unbreakable.? code protection is constantly evolving. we at microchip are co mmitted to continuously improvi ng the code protection features of our products. attempts to break microchip?s c ode protection feature may be a violation of the digital millennium copyright act. if such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that act. microchip received iso/ts-16949:2009 certification for its worldwide headquarters, design and wafer fabrication facilities in chandler and tempe, arizona; gresham, oregon and design centers in california and india. the company?s quality system processes and procedures are for its pic ? mcus and dspic ? dscs, k ee l oq ? code hopping devices, serial eeproms, microperipherals, nonvolatile memory and analog products. in addition, microchip?s quality system for the design and manufacture of development systems is iso 9001:2000 certified.
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