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RFM95 数据表(PDF) 77 Page - HOPE Microelectronics CO., Ltd. |
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RFM95 数据表(HTML) 77 Page - HOPE Microelectronics CO., Ltd. |
77 / 121 page Page 77 RFM95/96/97/98(W) Tel: + 86-755-82973805 Fax: + 86-755-82973550 E-mail: sales@hoperf.com http:/ / www.hoperf.com F = XOSC WIRELESS & SENSING PRELIMINARY DATASHEET 5.3.2. CLKOUT Output The reference frequency, or a fraction of it, can be provided on DIO5 (pin 13) by modifying bits ClkOut in RegDioMapping2. Two typical applications of the CLKOUT output include: To provide a clock output for a companion processor, thus saving the cost of an additional oscillator. CLKOUT can be made available in any operation mode except Sleep mode and is automatically enabled at power on reset. To provide an oscillator reference output. Measurement of the CLKOUT signal enables simple software trimming of the initial crystal tolerance. Note To minimize the current consumption of the RFM95/96/97/98(W), please ensure that the CLKOUT signal is disabled when not required. 5.3.3. PLL The local oscillator of the RFM95/96/97/98(W) is derived from two almost identical fractional-N PLLs that are referenced to the crystal oscillator circuit. Both PLLs feature a programmable bandwidth setting where one of four discrete preset bandwidths may be accessed. The RFM95/96/97/98(W) PLL uses a 19-bit sigma-delta modulator whose frequency resolution, constant over the whole frequency range, is given by: F STEP ---------------- 2 19 The carrier frequency is programmed through RegFrf, split across addresses 0x06 to 0x08: F RF = FSTEP × Frf(23,0) Note The Frf setting is split across 3 bytes. A change in the center frequency will only be taken into account when the least significant byte FrfLsb in RegFrfLsb is written. This allows the potential for user generation of m-ary FSK at very low bit rates. This is possible where frequency modulation is achieved by direct programming of the programmed RF centre frequency. To enable this functionality set the FastHopOn bit of register RegPllHop. 5.3.4. RC Oscillator All timing operations in the low-power Sleep state of the Top Level Sequencer rely on the accuracy of the internal low- power RC oscillator. This oscillator is automatically calibrated at the device power-up not requiring any user input. |
类似零件编号 - RFM95 |
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类似说明 - RFM95 |
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