AN744

M Author: AN744 FIGURE 1: Modular Mid-Range PICmicro® KEELOQ® Decoder in C DECODER PIN OUT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 NU NU VLOW LEARNOUT OUT3 OUT2 OUT1 OUT0 VDD VSS NU NU NU NU Lucio Di Jasio Microchip Technology Inc. MCLR LRNOUT RFIN NU NU LEARN NU VSS OSCIN OSCOUT NU NU NU OVERVIEW This application note describes a KEELOQ code hopping decoder implemented on a Microchip Mid-range Enhanced FLASH MCU (PIC16F872). The software has been designed as a group of independent modules (standard C source files "C" ). For clarity and ease of maintenance, each module covers a single function. Each module can be modified to accommodate a different behavior, support a different MCU, and/or a different set of peripherals (memories, timers, etc.). KEY FEATURES The set of modules presented in this application note implement the following features: Source compatible with HITECH and CCS C compilers Pin out compatible with PICDEM-2 board Normal Learn mode Learn up to 8 transmitters, using the internal EEPROM memory of PIC16F872 Interrupt driven Radio Receive (PWM) routine Compatible with all existing KEELOQ hopping code encoders with PWM transmission format selected, operating in "slow mode" (TE = 400 µs) Automatic synchronization during receive, using a 4 MHz RC oscillator NU TABLE 1: Pin Name RFIN FUNCTIONAL INPUTS AND OUTPUTS Pin Input/ Number Output 3 I Function Demodulated PWM signal from RF receiver Input to enter lear...