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ATA5771 Datasheet(PDF) 7 Page - ATMEL Corporation |
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ATA5771 Datasheet(HTML) 7 Page - ATMEL Corporation |
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7 / 219 page  7 9137E–RKE–12/10 Atmel ATA5771/73/74 3. Functional Description Figure 1-1 on page 2 and Figure 1-2 on page 3 show the interconnections between the micro- controller and the RF part for a typical application. In the recommended application circuits the clock output of the RF transmitter is connected to the microcontroller in order to be able to generate data rate with tolerance lower than 3%. The transmitter’s crystal oscillator (XTO), Phase Locked Loop (PLL) and clock generation are started using pin ENABLE. The Power amplifier (PA) is activated using the connection to the pin PA_ENABLE. The FSK modulation is performed due to pulling of the crystal load capacitance for this purpose the microcontroller out put port together with an external switch applies this modulation technique. For the ASK modulation the power amplifier will be switched on and of by modulating the PA_ENABLE pin due to the data. To wake up the system from standby mode at least one event is required, which will be performed by pushing tone button. After this event the microcontroller starts up with the inter- nal RC oscillator. For the TX operation the user software must additionally control just 2 pins, the pin ENABLE and pin PA_ENABLE. In case of the FSK modulation one additional connec- tion from microcontroller is necessary to perform the pulling of the crystal load capacitance. If ENABLE and PA_ENABLE are set to LOW the transmitter is in standby mode with the suit- able mode setting of the microcontroller (MCU) the power consumption will be reduced. If ENABLE is set to HIGH and PA_ENABLE to LOW, the XTO, PLL, and the Clock driver of the RF transmitter are activated and the VCO frequency is 32 times the XTO frequency. The Atmel ATA5771 and Atmel ATA5774 require typically shorter than 1 ms until the PLL is locked and the transmitter’s clock output is stable, while the Atmel ATA5773 requires time shorter than 3 ms for this progress. If both ENABLE and PA_ENABLE are set to HIGH the whole RF transmitter (XTO, PLL, Clock driver and power Amplifier) is activated. The ASK modulation is achieved by switching on and off the power amplifier via pin PA_ENABLE. The FSK modulation is performed by pulling the crystal load capacitor which will change the reference frequency of the PLL due to the data. The microcontroller modulates the load capacitance of the crystal using an external switch. A MOS transistor with a low parasitic capacitance is recommended to be used for this purpose. During the FSK modulation is the PA_ENABLE pin set to HIGH. To generate the data for the telegram the internal RC oscillator of the microcontroller is not accurate enough because this will be affected by ambient temperature and operating voltage. To reduce the variation of the data rate lower than 3% the clock frequency generated by the RF transmitter should be used as a reference. The MCU has to wait at least longer than 3 ms for ATA5773 after setting ENABLE to HIGH, before the clock output from the RF transmitter can be used. For ATA5771 and ATA5774 the MCU must wait longer than 1 ms until the clock output is stable. The clock output with the crystal tolerance is connected to the timer0 of the MCU. This timer clocks the USI to generate the data rate. In the Two serial synchronous data transfer modes will be provided by USI. This will be pass out with different physical I/O ports, two wire mode is used for ASK and the three wire mode for FSK. |
Similar Part No. - ATA5771_10 |
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Similar Description - ATA5771_10 |
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